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Framan 4.9

1. Measurement A C mode Data presentation Z versus Z olx kA File View Copy Plot Analysis Editdata Window Cell off after measurement pe Standby potential V 0 1000 ERA test procedure with dummy cell connect WEIT 11 Potential Potential W Title and Subtitle Pe procedure with dummy cell connect WEIfCN 4 850 Z ohm 1100 Status Messages HA Star E Edit procedure 2 Frequency Resp EJ Data presentation U Manual control 2 Screen Capture Sy 3 18 PM The screen consists of the following parts The FRA Manager window with a title bar and a tool bar The Manual control window This window is used to control all potentiostat galvanostat settings The Edit procedure window This window is used to modify experimental parameters When using FRA for the first time the default parameters are the factory settings Changed parameters are saved automatically at exit and appear as default parameters on the next occasion The Data presentation window This window gives a graphical display of the measured data and provides the entries to analyse and modify the data The Status window This window is used to start and stop a measurement procedure and to display system messages 12 User Manual FRA for Windows Version 4 9 These windows are explained in detail in the next chapter The rest of this chapter 1s used to walk through a num
2. s Mark two points on the straight line part of the impedance plot by clicking them After a data point has been clicked the frequency at which the data point is measured is displayed in red in the top of the Z versus Z window 9 Click OK on the Marker window 10 A slope of nearly 1 00 should be printed in the Linear regression window 1 Otherwise click the Set line option in this window to try it again 12 Click Close on the Linear regression window 13 Click Window on the Frequency Response Analyser manager window Select the Analysis results option to obtain a printed copy of the results 14 Close the Analysis results window 15 Click Analysis on the Data presentation window and select the option Find circle 15 Mark three points on the semi circle part of the impedance spectrum and subsequently click OK on the Marker window The results are displayed in the Find circle window Click Cancel to stop or Find circle to try again 16 User Manual FRA for Windows Version 4 9 17 Click Edit data and select Correct for Ohmic drop Type a value of 74 on the displayed window and click OK Now the so called electrode impedance is displayed Fig 6 Semi circle analysis Frequency Response Analyser olx Eile Method Utilities Options Project Window Help Method Potentiostatic freq scan Procedure FRADEMO amp Data presentation Z versus Z Lal File View Copy Plot Analysis Editdata Window Ferri fer
3. Chapter 3 The FRA windows 49 Fig 18 Window which appears after double clicking the axis labels Axis Labels Labels Position Format j O Decimal Above Axis Scientific Above Plot Engineering Below Plot J Set precision a Confirmation Text Parameters Fig 19 Window which appears after double clicking the data Plot Parameters Type EEN O Fill Area Line affributes Marker Attributes Shape Color Size a ie O Drop Line Style O Full Empty Empty Dot 3 7 Edit procedure window The edit procedure window consists of two pages On page 1 the most common parameters can be specified Page 2 contains the other parameters The parameters are divided in several sections 1 e pre treatment measurement potential comment title and subtitle A full list of the definition is found in the appendix The FRA data can be saved directly to disk while the measurement is in progress by specifying a direct output name The data will be written with the extension DFR 50 User Manual FRA for Windows Version 4 9 This option is useful for long duration scans and prevents data loss due to a failure of the power supply If no path is included the default data directory is used Please note that next to the parameter in this window the current ranges of the Autolab manual control window and the four parameters of the FRA manual control window will be stored as part of the procedure as w
4. Cs versus E View Copy Plot Analysis Editdata Window Ferri ferro 7 Click Calculate and then OK s Select View in the Data presentation window Click Potential scan plot and Cs vs E 9 Click the upper right button of the Cs versus E window as well as of the Data presentation window 10 Click Start and wait until the measurement is ready During the measurement the plot can be re scaled by pressing F4 1 Select View and click Potential scan plot 12 Click Select frequency and click in the part Frequencies not displayed those frequencies to be shown and click the upper button to bring the selected frequency to the part Frequencies selected Now click the OK button The selected frequencies are shown on the screen s Click Edit data Change all points Select Cs F and specify a value of 2 14 Click the Multiply button All capacitance values of the black coloured points are multiplied now This option can be used to correct for the surface area Click Close s Select Plot and click Resume as well as Automatic Now the original measured data are shown again 16 Select View again followed by clicking Potential scan plot and Y w versus E plot 17 Select Window in the Data presentation window and click Tile The two plots are shown now 18 20 21 User Manual FRA for Windows Version 4 9 Double click the upper left button of the Y w versus E plot This time the screen only shows the capacita
5. Procedure FRATEST lelx black E FRA test procedure with dummy cell connect WE c Status Messages J 15 Start E Edit procedure E Frequency Respons El Data presentatio U Manual control amp Screen Capture EV 3 20 PM 17 Click View again Select Y versus Y Now the admittance plot appears 18 Click Window on the Data presentation window Select the Tile option Now the impedance and admittance plot are both presented 19 Close the Admittance plot window 20 Click Window on the Frequency response 2 2 Manual control 1 Connect the dummy cell The red lead should be connected to WE c 2 Click Window on the Frequency Response Analyser manager window Select FRA manual control and FRA settings 3 Click the green led of the 1 mA current range Make sure that the check box of 1 mA is checked 4 Apply 1 V by moving the slider in the potential panel 5 Click the Cell on The current should be about 0 91 mA 6 Click the 1 kHz button of the Range panel in the FRA manual control window 7 Apply an amplitude of 0 01 V rms by moving the slider in the Amplitude panel s Click the Measure button on the FRA manual control window Inspect all the data presented on the active windows 14 User Manual FRA for Windows Version 4 9 Fig 4 FRA manual control a Frequency Response Analyser iof x le Method Utilities Options Project Window Help Meth
6. for x 1 the change in dc level is equal to the peak amplitude after exactly one period of the sine It shows that significant errors are found at low values of x A small dc ramp will give a significant error Conclusion Impedance measurements should be done under stationary conditions The dc current for potentiostatic measurements should be constant and for galvanostatic measurements the dc potential should not vary 78 User Manual FRA for Windows Version 4 9 Effect of measurement resolution The amplitude of the measured potential and current signals depends on the output of the potentiostat galvanostat The current range determines the amplitude for the current signal The setting of the amplifiers of the FRA also determines the amplitude of the final measurement The recorded amplitudes are shown in the FRA control window as well as in the Oscilloscope windows The maximum resolution is 100 however a much lower amplitude is often found The effect of varying amplitude or resolution of the current signal on the calculated impedance has been investigated Fig 25 Percentage error in the impedance as a function of the resolution of the current measurement The resolution is given in percentage Data presentation File Copy Plot Analysis Edit data Effect of resolution on error in impedance measurement 20 25 3 0 Resolution in E 000 Q 00 C The curve is valid for a resolution of the potent
7. BTAPNIES nn enden nleisselelsun uve cebsunte ses EE ES tes 5 6 19 42 48 H EN O O 7 E ON 5 6 30 I impeda ce SPSCUUM italia dales 12 15 OU ici obeule wanes 7 IR compensa ON tir taa 33 O NN 41 L linear regression OO 14 15 43 Load data i ee ir NON 20 M Manual Control ii a E SIES 5 11 13 14 31 34 A NN 36 Method iris li 8 12 16 22 30 57 63 64 MOUSE A 6 MS WIdO WS did 3 MS Word msn rappel bat eh ee hecha 5 35 36 MUET srein ee ei Bein E E EE E ehiinirernptsn 25 Mulder rere eee er AEE 36 63 MUX control erraten E E EE TE dro 25 O OMT ea A tad cata 16 45 Open procedure iii ia tod ds 19 OscilloScOpe WII WS cti a dad 14 P Pd a a Pash E sabes sea Pe E EA 27 Plot ici 12 16 17 40 plottitle cai dad ii tic 47 potential ati 16 17 22 30 33 35 37 38 39 40 50 54 57 63 64 potentiost t srecen Raise E E ben a a E A E bea A E E EN 5 11 19 Potentiostatic potential scan nen een enteo nano essen 22 Potentiostatic single potential u 2uuussesnsssessnnssnsnnssnnnsnnnnnsnnnsnnnnssnnnnnnnnnnnnsnnnnnnnnnsnsnnnsnonsnnnnsnansnnnnen 22 PHL ACE oan rss SN 5 pre tre tment n en isn Biene teat eset Geb emo E 50 54 55 57 58 64 Pant Ses Pow eed ced av gh Sayan E E E EE EEE EE EE EE SEEST 6 20 Print setup A eet ER te ee ee a es ee 20 DO dc dera Ten reisen R peri 26 27 30 Project W1Zatd ad 29 R INEO Mi LEKI DAAE Ea EPE EE is e e e to a NEA SN 8 9 33 54 56 Resume STO 40 S SAVE
8. Select DAC channel wih care DAC channel 3 may be in use by the BIPOT ARRAY or ECD module Do not use these modules together with RDE control DAC channel 4 may be used for 4C voltammetry and may therefore result in wrong applied potentials on the potentiostat Contact your distributor if you need more information Cancel In this screen you can configure the RDE Chapter 3 The FRA windows 25 MUX control The channel number of the SCNRI6A SCNR8A or MULTI4 module can be selected manually by the operator before starting the measurement procedure 1 Open the MUX control dialog by selecting MUX control from the Utility menu The dialog screen shown in the figure below will pop up Enable the checkbox Use Multiplexer Module Choose the desired channel Pressing lt Apply gt or closing the dialog screen will set the selected channel The active channel number will be indicated in the Manual control window 2 3 4 5 Fig 11 The MUX control window 4 Multiplexer control SCNR16A Currently selected channel Select Channell1 16 If you want to return to direct connections you can disable the Use Multiplexer Module checkbox Options Several options for data presentation can be specified Rescale after measurement perform autoscale and replot data when measurement has finished Rescale during measurement rescale and replot when necessary also during the measur
9. Convert button has to be clicked Subsequently the following columned ASCII or text files can be created Frequency value Z and Z value time of measurement Edc and Idc at the time of measurement Frequency value Y and Y value serial capacitance value time of measurement Edc and Idc at the time of measurement Potential value or current value Z and Z value time of measurement Edc and Idc at the time of measurement Potential value or current value Y and Y value serial capacitance value time of measurement Edc and Idc at the time of measurement The tm Edc and Idc can be left out of the file by unchecking the Include tm Edc and Idc check box Depending on the type the required ASCII file format one or more frequency potential or current value has to selected from the list box For each frequency potential or current a file is created The name of the file is the same as the data file name The files are stored in the same directory as the data file resides The extension depends on the type of file see Appendix A special type is the Mott Schottky file It contains a matrix of values for Z values for all frequencies and potentials The extension of this file is MOT Please note that data sets created before FRA version 2 4 will not contain any data for time Idc and Edc 22 User Manual FRA for Windows Version 4 9 Load calibration file
10. This option allows to change the calibration values to optimise performance for specific FRA2 modules This option is useful when different Autolab instruments are connected to a single computer Since the calibration files are instrument dependent they should be kept together The indicated number when starting up the FRA software should match the serial number on the instrument If one exchanges instruments on one computer the Load calibration file can be used to adjust the calibration file to the new situation Please note that the new calibration file does not have to be in the Autolab root folder It is advisable to be cautious with this command and only use it for the situation described above If you keep the computer and instrument as a pair after the initial software installation this option may never be necessary Delete files This option allows deletion of procedures and measured data files The File window only shows the procedure files A selected procedure will be deleted from disk together with corresponding data files A delete action cannot be undone Exit The FRA window will be closed and the program is exited The program settings are stored on disk Method The type of measurement can be selected with the Method menu The experiment parameters in the Edit procedure window will change depending on the selected type of measurement The following methods are available Potentiostatic single potential A frequenc
11. W 100 240 V 50 60 Hz Autolab with PGSTAT302N yes optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 51 5 x 41 6 x 16 cm3 18 kg 247 W 100 240 V 50 60 Hz Autolab with PGSTAT100 on request BSTRIOA only optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 52 x 42 x 17 cm3 21kg 300 W 100 240 V 50 60 Hz Notes 1 Measured at 1 mA current range 1 kOhm impedance high speed mode when applicable All specifications at 25 C Hardware specifications FRA modules e frequency range e applied amplitude 0 1 mHz to 50 kHz 0 2 mV to 0 35 V rms with steps of 0 1 mV potentiostatic mode 0 0002 to 0 35 with steps of 0 0001 times applied current range galvanostatic mode e resolution of DSG 1 in 65536 16 bits e Output impedance of DSG 50 Ohm e resolution of dual channel ADC 1 in 4096 12 bits e ADC input ranges 0 01 V to5 V 10 ranges software programmable FRA2 module frequency range applied amplitude 10 uHz to 1 MHz 0 2 mV to 0 35 V rms with steps of 0 1 mV potentiostatic mode 0 0002 to 0 35 with steps of 0 0001 times applied current range galvanostatic mode resolution of DSG 1 in 65536 16 bits output impedance of DSG 50 Ohm e res
12. Z o Zrei and Zim are the experimental data Zre wi and Zimo are the fitted calculated values In addition to Y the serial or parallel depending on representation R L and C values are computed see circuits These values do not have any special meaning and they simply belong to the set of results of K K test In particular they should not be associated with any serial or parallel elements present in the system or its equivalent circuit representation The detailed discussion of the Kramers Kronig test the theory underlying the choice Of parameters and a refined interpretation of the outcomes can be found in the previously mentioned article of Dr B A Boukamp It is advised to read this article before this option is used X i l Appendix IX Kramers Kronig test 89 Using the Kramers Kronig test Ea SI Load the data file FRADEMO from the AUTOLAB TESTDATA directory From the Analysis menu Data presentation window select Kramers Kronig test Choose whether impedance or admittance representation of the tested data should be used Modify the number of subcircuits if necessary default number of subcircuits is equal to the number of data points If necessary change the number of frequencies per decade using the extension factor default 1 i e the number of frequencies per decade is the same as in the measured data Choose the type of the test complex real or imaginary
13. at which the measurement has to be performed This input is only requested for the single potential or current method Repeat pre treatment before every The drop down menu appears from which the options no frequency and freq scan can be selected The latter option only appears in case potential or current scan is made no means that the pre treatment only takes place before the measurements Standby potential or current The potential or current applied as soon as the measurements have been performed Start potential or current The first potential or current of a potential or current scan This input is only requested for the potential scan method Step potential or current The potential or current increment between two successive measurements This input is only requested for the potential scan method Appendix III Definition of procedure parameters 65 Stirrer on during conditioning Switch on the stirrer during the different conditioning stages Synchronised measurement If checked the impedance measurement is performed after a waiting period equal to the Equilibration time This allows measurement at a fixed time after applying the dc potential or dc current For more information please read the chapter about the measurement sequence Stop equilibrium at threshold Enable the option to abort the equilibration stage when the Equilibrium threshold level is reached Time to wait for OCP The time you want to
14. channel simultaneous sample and hold analog to digital converters are 12 bits wide The maximum conversion rate is 200 kHz for the older FRA and 800 kHz for the current FRA2 The results of the conversions are stored in two memories each with 4096 words of 24 bits wide Thus each memory location can contain the sum of up to 4096 conversions The DSG and the ADC s are synchronised by using one clock crystal for both modules Chapter 2 Getting started with FRA 11 2 Getting started with FRA Connect the dummy cell box which is delivered with Autolab The red lead should be connected to WE c Switch the instrument on To start the program double click the FRA icon in the program manager The factory default windows of FRA appear Fig 2 Factory default layout of the FRA windows Frequency Response Analyser olx Eile Method Utilities Options Project Window Help Method Potentiostatic freq scan Procedure FRATEST Em Edit procedure of x m Manual control Edit frequencies Current range Settings Potential iR compensation a Page 1 Page q Orta Cell o Al EJ gt 4 gt F100mA High Sens at 000 y 00 Pretreatment O RX 10 mA First conditioning potential V O RIMA High Speed Duration s O A 100 uA O Current Equilibration time s O mw 10uA Potentostti d O Potential OR 1uA Repeat pretreatment before Pe 100nA every gt OT 10nA j O Time Potential iB comp Off
15. current should be given an analog output signal within the linear range of the current to voltage converter 5 V the cell impedance the ac output signal should have an amplitude high enough to be measured accurately but should also be within the linear range the applied frequency the frequency must be lower than the specified maximum frequency so within the bandwidth of the current range The system default maximum frequency is 15Hz for the 100nA scale 150Hz for the 1uA 1500Hz for the 10u A and 10 000Hz for the 1004 A Higher current ranges are not frequency limited In case you want to change them please contact Eco Chemie However please note that they have been carefully chosen and wrong values can deteriorate measurements The allowed gains of the amplifiers are also in the system definition file Possible values of the gains range from 0 gain 1 to 9 gain 512 The system default for the maximum gain is 128 for all current ranges The minimum gain is 8 for all current ranges except for the highest current range for which the gain is set to 1 Appendix III Definition of procedure parameters 63 Appendix Ill Definition of procedure parameters A C mode This is the most important measurement parameter It determines whether the applied ac signal is a sine with one frequency or whether it is a signal composed of 5 sines over one decade or 15 sines over two decades of frequencies The multi sine option is suitable for low fr
16. following types of files are used by FRA File PFR directory DFR FMA TXT EPR ECH F EN MOT SYSDEF40 INP SYSDEF40 TXT W_SIN W_SGNL FRA INI FRA2CAL INI Description Experiment parameters Measured data Project Analysis results Frequency Z and Z File format for EQUIVCRT program 2 potential no Frequency Y and Y 2 potential no Potential Z and Z 2 frequency no Potential Y Y and Cs 2 frequency no Mott Schottky data System definition parameters Description of SYSDEF40 INP Signal file for DSG FRA Signal file for DSG FRA2 FRA user settings FRA2 calibration data Appendix I FRA Data Files 59 Directory Default procedure Default data directory Default data directory Default data directory Default data directory Default data directory Default data directory Default data directory Default data directory Autolab directory Autolab directory Signals directory Signals directory Autolab directory Autolab directory Appendix II Bandwidth and Gains 61 Appendix II Bandwidth and Gains The bandwidth of the current follower depends on which current range is used In the system definition the highest applicable frequency for each current range is specified When the autoranging facility is used i e more than one current range is enabled in the Manual control window The optimal current range is determined by the de current the
17. likely to be observed in low frequency range In fact the K K test checks whether the measured data comply with the assumptions of Kramers Kronig transformation These assumptions are 1 the response is only related to the excitation signal 2 the response is linear or the perturbation is small e g lt 10 mV for non linear systems 3 the system does not change with time and 4 the system is finite for all values of including zero and infinity If the investigated system changes with time due to e g ageing temperature change non equilibrium initial state etc the test fails The idea of K K test is based on fitting a special model circuit which always satisfies K K assumptions to the measured data points If the measured data set can be represented with this circuit then the data set should also satisfy Kramers Kronig assumptions The special circuit used in the test is a series of RC circuits for impedance representation or a ladder of serial RC arrangements for admittance representation These circuits are shown below R Y L circuit for impedance representation circuit for admittance representation 88 User Manual FRA for Windows Version 4 9 By default the number of RC circuits or RC serial arrangements is equal to the number of data points If there is a chance that the measured signal was very noisy the number of circuits may be reduced to avoid overfitting and consequently including the noise in the mod
18. potentials or currents are plotted in different colours in one or more of the plot available types The potential or current values at which the frequency scans are displayed are shown in a drop down menu in the upper left corner of each graphical window The value selected from the drop down menu is the so called work data set All Edit and Analysis action are performed on this data set A maximum of four plot types can be displayed at the same time Each plot in a separate window In case a potential or current scan has been performed one or more of the following potential scan plots can also be selected Z versus E Draw a plot of the in phase impedance versus the potential or current Z versus E Draw a plot of the quadrature impedance versus the potential or current Y versus E Draw a plot of the in phase admittance versus the potential or current Y versus E Draw a plot of the quadrature admittance versus the potential or current Cs versus E Draw a plot of the substituted serial capacitance versus the potential or current wZ versus E Draw a plot of the in phase impedance 27f versus the potential or current Chapter 3 The FRA windows 39 wZ versus E Draw a plot of the quadrature impedance 27f versus the potential or current Mott Schottky Two types of Mott Schottky plots are available Rs Cs the experimental capacitance is calculated from a Rs Cs circuit in series Rs Cp Rp the capacitance
19. s labelst 22 sen cue da sede ae Rn EE au ele he lhe ote Rees 47 48 ARISTERT N a ns Re haa eal esos ONS ad ee adda deci ghia ne eae ek 16 41 B Batchinod ers 2b a IEEE ELLE EE an ee 26 BMP Oe ea nr a are a e A 36 B retie Control iettt Daisies ES A ales alte dedos OIE o E ies alo as 23 C cahbr tion de o de e ai 22 O 15 43 44 O RN 6 COLOUTS 525 O 47 48 Computern cook E AE si Rep Lele sbetnsch RR Delle ein 5 CONCEP Ces dace coeds NN 5 COD SUra AN 5 COM dun E E E E EE A 18 20 Cody isn R A E EAE E R A E ASS 36 EOpy zes sus using E R A A TA 27 36 51 COTTON 31 32 33 54 55 56 61 63 UA A e es Soe a ae 27 D Delete di o ERROR RRR Ri Ri Dh 22 double click 2233 65 SAB En 6 DS Get eG 3 ana I EE 7 8 9 55 56 E Edit fTEQUEN CIES pitt dida 50 Edit proce UTA Iii inte 11 Electrode Control ccccccccccccecscscececscececececscecsescecscscscscececececscececscscececseecececececececececececececececeeececececececeeecs 23 Extras pt tc pls la nar desde be lar a lore no EE An OE RR 22 F ARNO 6 RN 6 BP Lo 6 FP o e ee 6 a cad do 36 40 61 E A NO 19 35 frequency distribution cincel ini 17 50 G AN RN 5 11 Galyanost tic c rrent aa 22 Galvanostatic single current isise oie oeras e cono cono cn nono nooo nc rn nono nono o EEE nene recono cn nero nr rn nc rn nena s 22 graphical AAA cy seuebendiveapepeeven hegeuasvory coven iR 47 94 User Manual FRA for Windows Version 4 9 Sraphical setting ii aussi Ina dan ek rinnen 42
20. switched on automatic current ranging is no longer possible The only checked current range box becomes the actual current range 3 4 FRA Settings window The parameters printed in this window give information about the measurements In the Offset potential current panel the values with which the potential and current are compensated to remove the DC component from the signal Also the amplitude of the AC signal is given In the Results panel the applied frequency or base frequencies in case a multi sine is used as modulation the measured impedance and phase shift are displayed In the Resolution panel the resolution of the actual measurement of the AC current and potential are displayed the maximum value is 100 A low resolution say lt 0 5 yields a poor accuracy of the results The resolution of the measurement depends on the applied current range and the gains of the amplifier In case the resolution is too low and the gain of the amplifier is at its maximum a lower current range can be used However the applicable lowest current range depends on the applied frequency since the bandwidth decreases with lower current ranges If the resolution is 100 the measurement is done in an almost overload situation The highest allowed current range has to be increased See the Autolab manual control window The Gain panel indicates the gains which are used to amplify the I and E signal The maximum gain is 128 34 User Manual F
21. the Data presentation window allows the making of an analysis of the data In some cases the results are displayed in a special window which differs per analysis technique In all cases an analysis report is printed in the Analysis results window The Analysis results window contains all the results of the analysis of the data Only when the FRA Manager window is closed the Analysis results window is cleared The File option of this window allows the user to clear save or print the content of the window The Edit option allows the user to remove Cut the selected part of the text Text can be selected by keeping the left mouse button pressed and moving it over the window The Copy option copies the content of the window to the paste buffer The Paste option will include text from the paste buffer 52 User Manual FRA for Windows Version 4 9 It is possible to copy the analysis results to the data presentation graph in this manner Fig 21 Analysis results window ES Analysis results Eile Edit Linear regression Z ohm versus Z ohm File e Sautolab testdata frademo dfr Date 10 05 1998 Time 16 11 39 9 954E 1 d 1 08E 2 Intercept 3 392E 2 s d O9E 0 Chi square 572E 1 Corr coeff 997E 1 No points X begin Y begin X end 173E 2 Y end 512E 2 Y at X 0 3 392E 2 x at Y 0 3 407E 2 173E 2 749E 2 NDN MJ GC Find circle Circuit Rs Rp CPE File c Nautolab testdata frademo dfr Da
22. the current response with respect to this external source is measured The current signal from the rear of the Autolab instrument connector lout should be connected to Y using a BNC cable This software option is only available for instruments delivered after September 1997 Please consult Eco Chemie in case of problems 4 3 Time potential and current measurements After each impedance measurement the time dc current and dc potential are recorded The time is recorded from the start of the equilibration stage 4 4 Time scan It is possible to perform frequency scan of impedance measurements at a specified interval time at a fixed potential or current For this purpose the Method menu on the FRA manager window contains the option Time scan for both the potentiostatic as well as the galvanostatic mode The minimum interval time is at least two seconds but will depend on factors like the number of frequencies to be measured the frequency itself the minimum cycles to integrate and the maximum time to reach steady state see the FRA manual control window In case the interval time exceeds the specified value a message will be given but the measurements will continue The time at which a measurement is done is stored in memory for every single frequency but on the graphical window the whole frequency scan is plotted at the time at which the latest frequency in the scan is measured 54 User Manual FRA for Windows Ver
23. to the measured data using the non linear least squares method The equivalent circuits can be defined by the user using Circuit Description Code It is possible to define elements with fixed values as well as constraints for values of fitted parameters This option is based on the work of Dr B A Boukamp as first published in Solid State Ionics 20 1986 31 44 and coded in the program EQUIVCRT by the same author Please refer to the Appendix for more information about this option Edit data Change all points All the data displayed in the focused plot window can be changed however the change only effects the displayed data not the work data This means that the changed data cannot be saved and also newly created plots will be based on the unchanged work data Correct for ohmic drop All data points can be changed using this option A value for either Z Z or the potential current or time can be given Subsequently all loaded plots will be updated with newly calculated values With the Resume option of the Plot menu the originally measured data will be reloaded The Save work data option of the File menu can be used to save the modified data set Delete points An option is available to remove points from the plot This option can be used to remove spikes from the measured data The removal will be activated in all loaded plots With the Resume option from the Plot menu the original data set will be plots The Save work data
24. wait for acceptance of the Open Circuit Potential If this time has expired the program will continue using the OCP measured at that time If this parameter is O zero the program will not continue unless the Accept button is pressed If O zero is specified in a procedure that is used in a project the program will wait for 1 second and will use the OCP measured at that moment Title and Subtitle Two lines of text to describe the experiment These lines are the same as the ones displayed above the plot Appendix IV Combination of GPES and FRA 67 Appendix IV Combination of GPES and FRA The FRA and GPES programs can be used at the same time Moreover a FRA project file can be executed from GPES The command FRA Start lt filename gt is available for this purpose However in general it is important to note that both programs share the Autolab instrument and the graphics part of the software Moreover both programs require a considerable amount of the system resources This means that when both programs are active hardly any system resources are left Practical rules are The computer should be equipped with 32 MB RAM It is not possible that both programs measure and control the Autolab instrument Before the FRA program starts measuring the sleep mode in GPES is automatically switched on This means that the GPES screen is no longer updated Do not use function keys when both programs are active because they will cause actio
25. will be printed in the Results window One line per command The following commands are allowed lt string gt comment rem lt string gt comment Procedure Open lt filename gt open a procedure file Procedure Start start the execution of the procedure Procedure SaveAs lt filename gt save a procedure file Dataset Open lt filename gt open a previously measured data file Dataset SaveAs lt filename gt save the measured data Dataset AutoNum lt n gt enable auto numbered files names starting with number lt n gt Dataset AutoReplace specify the string which should be lt string gt replaced by a number in the lt filename gt for auto numbered files System Run lt filename gt execute an other program System Beep give a beep Print Procedure make a hardcopy of the experiment parameter Print PLOTZZ print a hardcopy of the plot of Z versus Z Print PLOTY Y print a hardcopy of the plot of Y versus Y Print PLOTBODE print a hardcopy of the Bode plot Print DATA print a hardcopy of the measured data 28 User Manual FRA for Windows Utility Channel lt n gt Utility NextChannel Please note The last 2 commands are available in the GPES and FRA programs However for FRA projects that are called from within GPES projects all channel switching commands in the FRA project scripts are ignored In such cases the GPES project will have exclusive
26. 0 10 Y N Y N Y N Y N Y N Appendix VII Theoretical considerations on the performance of FRA instrument 75 Appendix VII Theoretical considerations on the performance of FRA instrument The performance of the FRA impedance analyser depends partly on the construction principles and partly on the setup parameters i e the integration time the number of integration cycles and the time to reach steady state These parameters can be specified on the FRA manual control window In this appendix it is investigated how the measurement results depend on these parameters Moreover this appendix can be used to compare the measurement principle of the FRA with other impedance analysers All the data presented in this appendix result from numerical simulation Effect of integration time on noise rejection The effect of integration time on noise rejection is determined by numerical simulation The transfer function of the FRA module as a function of the frequency normalised with respect to e g 1000Hz for a different number of integrated cycles has been calculated The transfer function is calculated by performing Fast Fourier Transformation on the signal generated with frequency f The amplitude found at frequency fo gives the transfer function Frequency fo is in fact the frequency at which the impedance should be measured The transfer function shows the theoretical noise rejection ability Fig 22 Transfer function of the FRA module as a functio
27. 2 80 mA 12 V yes yes 5V 0 2 of setting 2mV 150 uV 300 or 30 uV 10 nA to 10 mA in seven ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lus high speed high stability gt 100 GQ lt 8 pF lt 1pA gt 4 MHz n a no no potential and current no no Appendix VI Specifications 71 Autolab with PGSTAT12 250 mA 12V yes yes 10V 0 2 of setting 2mV 150 uV 300 or 30 uV 10 nA to 100 mA in eight ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lt 500 ns high speed high stability gt 100 GQ lt 8 pF lt 1pA gt 4 MHz depending on selected range 0Q 200Q at 100 mA range to 0Q 200 MQ at 10 nA range current interrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes multipleWE option Autolab with PGSTAT302N EZA 30 V yes yes 10 V 0 2 of setting 2 mV 150 uV 300 or 30 uV 10nAtolA in nine ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA gt 1 MHz lt 250 ns with external source high speed high stability gt 1 TQ lt 8 pF lt 1pA gt 4 MHz depending on selected range 0Q 20Q at1 A range to 0Q 200 MQ at 10 nA range current i
28. CALA meton e pei eins 20 Save procede coi EEE E EEE Een E EEE T E E E ia 20 Save procedure Asia e it E E tn 20 Save Wwork AA E RN 36 SENRI OA riscos ida le Sg 25 Appendix X Index 95 SENRSAY nenn ans status El ae Eu RED Io anna Ah aie ane 25 Select frequency iaa asian ee AL Alb iii else 17 39 Select potential cg Currents iisen essen esse e r EE E OVER eei 37 SS NO 12 14 15 40 43 44 SOQUENCS e a rn docencia TE E doi iden iii ici 54 57 A NON 5 33 35 42 55 58 O E suid eisen bireelbenenhekende 36 StAtUs Da did lia da daria 31 OA 47 synchronized Measurements is 57 58 64 T Technical backgrounds ii as da a de Batis da bea ds do 55 textbook8s near cedex oh Men ed Gu cena ee She ea ooh abe Gh eb ea cep dunen eee odanl R bab cee mabee nao hen 7 O 5 11 30 55 WIEDER he leh AG ee ea IS Sh Bech a ek GAY Fa Sinks alee oe A ee Oeil oh oe Se 25 types OF E NN 59 U Ult votada ill id 23 V ATEA T EE RN 36 VIS WINS data nn sten EE S cs EEE AEA E E EE EA E EEEE EE EEE EA S 47 W WME 2 252884 Hase E an Ru ena 36 Z
29. CATIONS ccccsssssssssssssesssssssersesessessssessessesessesseseesesesesessesesessesesersesees 71 Hardware Specific ations 20 A A Ad da dai 72 S ftw re specifications iii A EEEa did 73 APPENDIX VII THEORETICAL CONSIDERATIONS ON THE PERFORMANCE OF FRA INSTRUMENT sssssssssssssssrsesssssssessscersssscsnsssccssensesceseesescesensescssensescesensescssensssesscsesseseesesseseesessesess 75 Effect of integration time on noise rejectiON ooocoononnccconennnnnncnnnnnnnncnnnononnnc cane n ron nc cane nono nc cannn ran nccnne 75 Effect of noise on impedance measurements c ooococccocnnoncnnnconanonocnno nono nn nena nono conan nn nn n anar cn ne cone cn neon neon 76 Effect of non stationary dc current uceseerseesseensnennesnnernnesnnesnnesnonsensnensnnnsnnnnnnnnnnnernnennnesnnesnan nn 77 Effect of measurement resolution uczzuesesseessnessnsenssnensnensnnensnnnnnnnensnnennsnonsnnnnnsnensnnennnnonsnnnnnsnnnsnnn 78 APPENDIX VIII FIT AND SIMULATION csssssssssssssssssessessssessessesessesseseesersesessesseseeessesesersesees 79 Circuit description code dl ai ent 79 File Mei tetas 80 Edit menu tes ents amp 1 Options MENU e ti iia 8l Using fitand simula is noted os ante ota ies 83 APPENDIX IX KRAMERS KRONIG TEST 2022022020000000000000000002002002002002000 000000000000 000000 000000000000 87 The Kramers Kronig test ccccccssccssscscsscceescecssecesscecsscceeacecsaceeeacecsaceseaeecsaeeesaeecaceeeaeecsaceeeaaeceee
30. Press Start test button To leave the window press Close button Appendix X Hydrodynamic Impedance Measurements 91 Appendix X Hydrodynamic Impedance Measurements Autolab instruments equipped with the FRA2 module can be used for hydrodynamic impedance measurements The required external connections to the BNC connectors at the front panel of the FRA2 module are signal out to the input of the controller of the rotating disk electrode RDE Y to the output of the controller of the RDE X to the current output marked Iout at the rear of Autolab These connections have to be made using shielded BNC cables The signal out of the FRA2 module is used to modulate the rotational speed of the RDE The impedance analyser part of the FRA2 measures the signal from the RDE controller and the current intensity from the potentiostat galvanostat When signals coming from the X and Y external inputs on the front panel have to be measured this can be specified in the FRA manual control window The check box Use external inputs in this window must be checked The message External inputs are used appears after the START button has been pressed Appendix X Index 93 Index A O esis OE RAE RRR BRERA 7 8 9 56 57 Analysis RN 51 Automatic mercury drop electrode eeeeseceescecsseceeececeseceeccecaccesceecacesceecsaeceneecsaeeeeeeecsaeceeneecaeeeeee es 57 AXIS ANNOTATION NN 36 AXIS description 5 32 NN 47 ax
31. RA for Windows Version 4 9 3 5 FRA manual control window The FRA manual control window makes it possible to apply an ac signal to the electrochemical cell It consists of several panels In the range panel a frequency range can be selected With the Frequency and Amplitude panel below the frequency and amplitude of the ac signal can be selected Both panels contain a slider and a text box The slider box can be dragged to change the value A click on the arrows or on the slider bar itself changes the value by a distinct increment The increment is different for the arrows and for the bar The input fields below determine how the measurements are done They require some extra explanation The integration time The minimum period during which the signals are measured The longer this period the more accurate the result will be The minimum time of measurement is equal to one cycle of the in case of multi sine lowest frequency Thus 1f the cycle time is longer than the sampling time the sampling time will automatically set to the time of one cycle A generally suitable value equals one second If the time to measure the minimum number of cycles see below is larger than the specified integration time the actual integration time will be determined by the minimum number of cycles The minimum number of cycles to integrate The minimum number of ac signal periods during which the signals are measured The more periods the more accurate the r
32. Set line button is clicked In case the plot type is such that a left as well as a right hand Y axis is displayed an extra panel is added to the Linear regression window where the user can select on which data the linear regression should take place Find Circle The Find circle option makes it possible to fit a semi circle through a part of the measured curve When the option is selected two windows appear One is the Find circle window and the other is the Markers window When the begin centre and end point of the circle have been marked on the measured curve and OK is clicked on the Markers window a semi circle is drawn through the marked points The slope of the 44 User Manual FRA for Windows Version 4 9 line dY dX the intercepts i e Y at X 0 and X at Y 0 and several other helpful data More semi circles can be drawn when the Find circle button is clicked If the Find circle option is not appropriate for a certain plot type 1t can not be selected For the plot type Z vs Z the program calculates the values of Rs Rp and CPE assuming an equivalent circuit with a CPE parallel to a resistance Rp and a resistor in series with this combination The impedance of the CPE is Z 1 i CPE Fig 16 The Rs Rp CPE equivalent circuit For the plot Y vs Y the program calculates the values of Rs Rp and r where r is the radius of the semi circle Find minimum and maximum The Find minimum and maximum option shows the mini
33. User Manual for Frequency Response Analysis FRA for Windows version 4 9 Eco Chemie B V P O Box 85163 3508 AD Utrecht The Netherlands Copyright 2007 Eco Chemie Table of contents 3 1 PRINCIPLES OF OPERATION cccssssssssssssessrsessessssesscssrsessessssessecsssessssssessccessessesensnsseseneesenses 5 LUPI is 5 1 2 The A O 5 1 3 The instrument and hardware description ee eee cee ceeecseeeeeeeeeeeeeeseeecesecesecaecsaecsaecaeesaeeeaeeeeeees 7 2 GETTING STARTED WITH FRA eesussesnesnesesnennenesnennenennennesennennenennennesennennssennenussesnennssesnenansennes 11 2 1 Recording an Impedance spectrum eesceesecessceceseceeseeceneeeeneecaeeesaeecsueeesaeecsaeeeeaeecsaeeseneecsaeeeeneees 12 2 2 Manbal control occasion abrio 13 2 3 Data manipulation with FRADEMO cnsessessnesnnesnnesnnesnonsnensnonsennnennonnnnnnnnnnnennnennnennnennnn nennen 14 2 4 Measuring double layer capacitance as a function of potential ooooncnncnncnnccnncnconnnonoconocnoconocnnonnss 16 3 THE FRA WINDOWS zusscsnensennenesnennenennenennennenennennenennennenennennenennennenesnennesennennesesnennssennennssesnenussennen 19 3 1 FERA Manager WOW a ces dee Lacan sa sn ee eee 19 File AA E ON 19 AI A O NAS 22 Utilities stehen sa rii a R O a OK tadas denen dia o E RAE ETC SOE yeaa hen indonesia anio aio sa Sida 23 Options esce E E tithe bevaa sets da 25 Projet orriaren seia ta ari ene EE OA aE tetas aR EE aa ESR REEE K ASES A eE
34. Volume lt Burette number gt lt Dose volume gt dose a specified volume to the specified burette Burette Fill lt Burette number gt Fill the burette Burette Flush lt Burette number gt lt Number of flushes gt flush the burette Burette Reset lt Burette number gt Will give a reset command to the burette lt string gt line of text lt filename gt a filename without extension but including a directory name A special case occurs when the measurements are done with respect to the open circuit potential Normally the user is asked to click the Accept button but in automatic mode the program continues by itself Project wizard The Project wizard provides an easy way of editing and or defining a project This option allows the user to pick project command lines from a list of all commands insert them in a project and define the parameters The window below gives a project Wizard overview Fig 12 An example of a project inside the Project wizard es Fra C Autolab T estD ata Demo01 insert This a demonstration projec The project executes a procedure stores the data and prints the procedure Category Command Insert gt gt Start Save s Delete lt lt If you have installed the Autolab application programs in another directory than C AUTOLAB the path in the ProcedurelOpen DataSetlSave4s and DataSet Open command lines Please connect the dummy cell using WE c Misce
35. a AEIR O RTE EER aT 26 WindOW AA TONO 30 A AAN 30 TOOU DG AAA E O RATON 30 3 2 Status DA a ii ici 31 3 3 Autolab manual control WINdOW oconoccconnconocononononnnonnnnnnnnnnnnnnonnnco recono cn ncon conoce nn ncnn crac rin nnnncnnncn anna nes 31 CUTTENE TANDE mo ia 31 SEINES aii tt ii ia 32 NOSE MATA A A usa yuvense ecvensauvertuadynnee 32 VA A E sae Aa ene ah Hag Te see runs EU aaa SEA gaa oe 33 iR compensation not yet possible oooononincnnoninonnnannonnnonnnnncnnn cono EE nn nora no EE SES E neo 33 SE Window A NO 33 3 5 FRA manual control window ueeeesnesnessnensnensnensennnnnnnnnnnsnnennnennnennnesnensnonsnensnensonnnonnennnnsnnrnnenn 34 3 6 Data presentation window oooconoccocnconnconononccnnocnnonnnonnnonn nono non nano none EOE EESE EEE are EEEo Enes K cane SNE SNE eee 35 COP isa 36 MT ns 36 Save WOTKAALG A EA 36 Met dt 36 A NAAA 36 Pl a a eo eee EEE LE EHEN e as sees 40 ANAIS neta i 43 EUR GILG a tn Santee eae ae 45 Editing graphical items and viewing data cssuessesssessnesnnesnnesnensensnensnnnnnnnnnnnnnnnennnennnesnnennan nn 47 327 Edit procedure A O een 49 PONTOON ita tienes 50 Edit frequencies n en nannte tien 50 3 8 Analysis tesults WIndoW u lesen est sonen een 51 4 MEASUREMENTS 2uc2u0seonenneneonennenesnennenennennenennennenennennenennennesennennenesnennssesnennssesnenussesnennssesnenassennes 53 AJ Advice ON MEU MEM Sinai 53 4 2 Internal External measurements 00 ee ee
36. a higher noise level on the potentiostat Project The Project option allows the execution of a large number of electrochemical experiments unattended A project encompasses a number of tasks which have to be executed sequentially Sometimes this is called batch mode processing A measurement procedure is normally activated by clicking the Start button in the lower left corner It is also possible to start a procedure by creating and subsequently executing a project A project can be created by selecting the Project edit option First you have to indicate whether a new project should be made New option or an existing project file should Chapter 3 The FRA windows 27 be opened Open option An example of a project is delivered with the FRA2 program in the testdata directory After editing a Project it can be stored on disk under its current name Save option or under a new name Save as option When Edit is selected the Edit project window appears with two options on the main menu bar The Check option checks whether there are syntax errors in the project commands The Edit option provides the standard Cut Copy and Paste option Below you will find the Project script language definitions and rules Project command rules Both upper and lower case characters can be used in command lines Space characters are ignored If during the execution an error occurs the project continues with the next line An error message
37. ailable elements and shows examples of circuits and their CDC s Fit control parameters Opens a window in which fitting related parameters like convergence criteria iteration limit and the type of fit can be set Maximum change in X scaled this is one of the convergence criteria Fitting will not be finished until the absolute change in the chi square parameter including weight factors will be lower than this value The default value is 0 001 Maximum number of iterations fitting will always stop if this number is exceeded The default is 50 Number of iterations per fitting step the fitting step finished by displaying a new data set and update of the parameter set on the screen can consist of a single or multiple iterations This option is useful if the program is running on a relatively slow computer because update of the screen takes some time so increasing the number of iterations per fitting step can result in a slight improvement of fitting speed Maximum number of iterations giving no improvement if during the fit there is no change in the specified number of consecutive iterations Y value and other convergence criteria are still not satisfied the program stops with an appropriate warning It usually suggests that the model is not appropriate no further improvement can be obtained while the Y value is still too high The recommended action is to change the CDC or 1f the fitted curve differs very much from the ex
38. amined data set to try other starting values for fitted parameters Use weighted fit if this box is checked each point is multiplied with a weight factor equal to the inverse of the square of the impedance modules i e w 1 Z Z If this box is empty weight factors for all points are equal to the inverse of square root of mean impedance modules It is important to note that in addition to the explicit convergence criteria i e max change in X there is an implicit criterion that the change in the parameter value during one iteration should not exceed 0 5 Options menu The following items are available in this menu 82 User Manual FRA for Windows Version 4 9 Select frequencies Using this option one can select the frequencies used in simulation or fitting Use constraints The fitting procedure uses internal default constraints for maximum and minimum values of parameters If these limits should be changed the Use constraints option should be activated The limits can then be set manually in the parameter editing panel in the middle part of the Fit and Simulation window Show covariance matrix This option displays a covariance matrix after a successful fit has been completed In the covariance matrix the diagonal elements are unity and off diagonal terms are a measure of covariance interdependence of the parameters In general the off diagonal values should be small compared to diagonal elements If la
39. ase and quadrature impedance versus the frequency Z versusvo Draw in phase and quadrature impedance versus square root of 27f Z versus 1Nw Draw in phase and quadrature impedance versus one over square root of 27f Y versus Vw Draw in phase and quadrature admittance versus square root of 27f Y versus 1Alo Draw in phase and quadrature admittance versus one over square root of 27f Y versus Y Draw quadrature admittance over 27f versus in phase admittance over 27f Epsilon plot Draw quadrature versus in phase permittivity after specifying the geometric capacitance being the capacitance of the empty cell The permittivity is defined as epsilon Y iwC epsilon i epsilon Z versus Z Draw in phase versus 27f times quadrature impedance Z versus Z 0 Draw in phase versus quadrature impedance over 27f Z versus Z Draw 27f times in phase versus 27f times quadrature impedance Select potential or currents When a potential or current scan has been performed the option Select potential or Select current can be chosen A window appears from which one or more potentials or currents can be selected or deselected The frequency scans measured at the selected potentials or currents will be shown 38 User Manual FRA for Windows Version 4 9 Fig 14 Select potentials window m Select potential s Not selected Selected 100 Y Cancel The data measured at the selected
40. aves a lot of time thus allowing the measurement of more reliable impedance data in case the behaviour of the electrochemical cell is time dependent Each of the two parts FRA DSG and FRA ADC consists of two boards The 64 kB RAM of the digital signal generator DSG is loaded from the computer While loading the LED marked load DSG is on The memory is loaded with the digital representation of the signal to be applied The 16 bits words are loaded from the hard disk drive The 12 bit multiplying DAC is used to control the amplitude of the output signal of the DSG The maximum amplitude of the DSG peak to peak equals 3 5 V FRA2 or 10 V FRA This mDAC makes it possible to set the output of the DSG with a resolution of 1 in 4096 Since the signal is divided by ten inside the potentiostat galvanostat the Chapter 1 Principles of operation 9 maximum amplitude peak to peak equals 0 35 V FRA2 or 1 V FRA The resolution of the applied signal is better than 0 1 mV The output of the DSG is available at the BNC plug dsg out or signal out As long as the contents of the RAM are used to set the 16 bit DAC the LED signal on will be on The output signals of the potentiostat I current output and E potential output are filtered and amplified The two identical amplifiers have software programmable gains of 1 2 4 8 16 32 64 128 256 and 512 The filter is a programmable 8th order Butterworth low pass filter The two
41. ber of examples that come with the FRA program These examples give you an idea of the possibilities of the program Please follow the instruction per example in detail It is assumed that you have experience with the GPES program Otherwise please first read the chapter Getting started with GPES of the corresponding manual 2 1 Recording an Impedance spectrum Click the Method option in the upper left corner of the screen Click Potentiostatic Click Single potential Click File option in the upper left corner of the screen Click Open procedure Type Autolab testdata fratest pfr Press ENTER Click View on the Data presentation window Click Z versus Z Click the upper right button of the Z versus Z window Click the upper right button of the Data presentation window Connect the dummy cell The red lead should be connected to WE c Click the Start button in the lower left corner of the screen Click during the measurements on the Plot option of the Data presentation window Click Automatic The graph rescales 5 Click during the measurements on both greenish toolbar buttons They allow you to inspect the ac sine waves and their frequency spectrum s After the measurement a semi circle is displayed o 0 NN DO oO A od N 0 Nn O Chapter 2 Getting started with FRA 13 Fig 3 Semi circle in impedance plot a Frequency Response Analyser _ ol x Eile Method Utilities Options Project Window Help
42. ccompanied by current values of their parameters the error estimate appears after the successful fit and the information whether the parameter is fitted or kept fixed When CDC is modified the values of element parameters are defaults used as start values If an element from the list is selected its parameters and settings can be edited in the parameter editing panel directly below the element list Panel for parameters editing In this panel the full description of the element selected in the list above is available and can be edited The values of parameters can be changed and the parameter can be made fitable or fixed If the Use constraints option Option menu is selected the Appendix VIII Fit and Simulation 83 limiting values for the parameters can be adjusted otherwise internal defaults for maximal and minimal values are used Fit panel This panel allows to choose whether fitting and simulation should use impedance or admittance representation of the data In the lower part of the panel the status of fitting is displayed iteration number fit finish error indication together with the value of Y Fit Simulation switch Using this switch one can choose between the fitting function and the simulation function When simulation is chosen the buttons Simulate and Close will appear When fitting is chosen three buttons are available Fit Stop Fit and Close Using fit and simulation Fitting of equivalent circuit to
43. ck box indicates whether the current range can be selected 32 User Manual FRA for Windows Version 4 9 Only a joined column of selectable current ranges is allowed The software always checks whether the row is closed If a range separated from another range is checked the intermediate ranges are checked automatically When a check box is clicked again the check disappears The allowed current ranges are stored on disk as part of the procedure The highest applicable current range for autoranging during potentiostatic measurements the advised highest current range depends on the lowest measured impedance of the cell In general the lowest measured impedance must be higher than 0 2 current range e g 20 ohm with a current range of 10 mA In normal application the highest current range can be 1 A with the PGSTAT20 30 100mA with PGSTAT12 100 or 10 mA with the PGSTAT10 Settings With the buttons in the settings panel the PGSTAT can be controlled The text on the button represents the current situation The following buttons might appear depending on the type of potentiostat galvanostat Cell on off allows to switch cell on or off In the off position the connection of the potentiostat with the potentiostat galvanostat is broken so no current can flow between the counter and working electrode High Sens off on This button has limited functionality in the FRA software With High Sens on the displayed value of the de current is improved
44. control over the channel selection Utility Delay lt n gt Repeat lt n gt EndRepeat Message string ForAllChannels lt filename gt DIO SetMode lt Connector gt lt Port gt lt Mode gt DIO SetBit lt Connector gt lt Port gt lt n gt lt Bit gt DIO SetByte lt Connector gt lt Port gt lt n gt DIO WaitBit lt Connector gt lt Port gt lt n gt lt Bit gt DIO WaitByte lt Connector gt lt Port gt lt n gt Version 4 9 sets the active channel to lt n gt The MUX will be automatically enabled when necessary increase the active channel number with one If the channel is not available the active channel number is set to 1 hold the project for lt n gt seconds With these commands you can repeat an enclosed sequence of instructions multiple times You can nest loops maximal 5 times Give a message and wait for click on OK executes the active measurement procedure for all available MUX channels and store the results in the lt filename gt adding 3 characters to the filename as channel number counter for example fname001 fname002 etc set the mode of a port of the DIO set a single pin of the DIO on or off set a port of the DIO to the specified value wait until a single pin of the DIO is set on or off wait until a port of the DIO is set to the specified value Chapter 3 The FRA windows 29 Burette Dose
45. de rms value of the ac signal In case of potentiostatic measurements a general applicable value equals 0 01 V The value should be so low that non linear effects are avoided Amplitude limits are normally 0 0002 V and 0 35 V In case of galvanostatic measurements the ac current amplitude should cause a potential response at which again no second harmonic effects are found However some specific measurements e g in case of very high impedance s require increased ac signals Chapter 3 The FRA windows 51 In case it is unknown at which amplitudes non linear effects occur some measurements can be performed while monitoring the frequency domain plot Non linear effects will give higher amplitudes at frequencies higher than the applied frequencies The software provides the button Show hide FFT spectrum in order to monitor the amplitude as a function of frequency Fig 20 Edit frequency window Edit frequencies T Parameters Sub scans Begin frequency 10000 0 Hz Distribution End frequency 0 1 Hz Linear Sub scan 3 Number of freq 50 Square root Sub scan 4 Sub scan 5 Amplitude rms 01000 Y Logarithmic Calculate l Frequencies Nr Frequency Hz Amplitude V 1 9999 99 01000 2 7905 96 01000 3 6250 5 01000 4 4941 702 01000 5 3906 965 01000 6 3088 872 01000 7 2442 034 01000 8 1930 689 01000 3 8 Analysis results window The Analysis option of
46. e first green LED or a grey background is shown The VU meter for the current signal is only active when the cell is switched on The VU meter for the potential signal is also active when the cell is switched off i e no Chapter 3 The FRA windows 33 current can flow During the execution of the procedure except for pre treatment stage the VU meters are inactive In case more than 4 LED s of the VU meter are on it is advised to take precautions You can select a higher current range or minimise the noise of your electrochemical cell High voltage noise levels are often caused by the reference electrode Potential The Potential panel contains a slider and a text box With these tools the applied potential can be specified The slider box can be dragged to change the value A click on the arrows and slider bar changes the value by a distinct increment The increment is different for the arrows and for the bar In the two panels below the measured current potential and time can be displayed depending on the option button selected iR compensation not yet possible The iR compensation panel appears only when the Autolab is equipped with a PGSTAT12 20 30 100 potentiostat galvanostat In order to perform iR compensation the iR compensation button on the Settings panel should be switched to R comp on Subsequently the ohmic resistance can be specified by using the slider or by typing in the textbox Note that when the R compensation is
47. e treatment has to be performed before every frequency 4 The dc potential or dc current is applied and the filter is set to the proper cut off frequency The ac signal is applied The timer is set to the equilibration time and waits until the timer is ready If the measurement is synchronised the timer is set to the equilibration time minus 1 second but the program continues without waiting for end of timer 5 The gains of both amplifiers are set The current range is set In case of the first measurement the Highest current range In all other cases according to calculated optimal current range depending on last measured results If the measurement is synchronised the program holds until end of timer is found Now the timer is set to one second s At higher frequencies higher than the minimum frequency for autoranging see Appendix I the gains of both channels are increased until an overload is found and then decreased with a factor of 2 At lower frequencies the gains are set according to the previous measurement 7 Ifthe measurement is synchronised the program waits for end of timer and waits the specified time needed to reach steady state of the ac response s The measurement is performed and results are calculated If an overload is found the gains and if necessary the current range are corrected and measurement is repeated at step 2 If the resolution of the measurement is too poor the measurement is repeated if a more optimal
48. edance versus time 40 User Manual FRA for Windows Version 4 9 Z Phi versus t Draw impedance and Phase shift versus time Y Y versus t Draw in phase and quadrature admittance as a function of time A maximum of four plot types can be displayed at the same time Each plot in a separate window Plot The Plot option contains all kind of possibilities to manipulate the graph like plot refresh automatic scaling zooming or display of a previously measured signal Sometimes not all options are selectable because they are not applicable or intervene with current active data analysis options Also when the execution of a procedure is going on not all options are selectable Some sub options require explanation Automatic The plot will be scaled automatically Some plots i e Z versus Z and Y versus Y will be scaled in such a way that both axes have a similar division so that a semi circle can be displayed correctly Resume The Resume option makes a fresh copy of the measured data into the Data presentation window Zoom Clicking the Zoom option has the same effect as pressing the right mouse button When this option is activated a magnifying glass appears When subsequently the left mouse button is clicked and held down a Zoom window can be created Set window This option allows to select part of the data set for further editing of data or data analysis Only the selected range of data points remains visible on
49. eeaeees 87 Using the Kramers Kronig test poniesienie saes akei e E Ea oneik ae aa Nap Eaa s 89 APPENDIX X HYDRODYNAMIC IMPEDANCE MEASUREMENTS csccsssssssssssssssssssoeees 91 Chapter 1 Principles of operation 1 Principles of operation 1 1 Preface Autolab and the Frequency Response Analysis system software FRA provide fully computer controlled electrochemical impedance spectroscopy This powerful technique can be used in the study of for example electrode kinetics electro deposition corrosion and membranes The instrument is controlled by a personal computer The Autolab configurations nn by FRA are Autolab with potentiostat galvanostat PGSTAT10 and FRA modules Autolab with potentiostat galvanostat PGSTAT12 and FRA modules Autolab with potentiostat galvanostat PGSTAT20 and FRA modules Autolab with potentiostat galvanostat PGSTAT30 and FRA modules Autolab with potentiostat galvanostat PGSTAT100 and FRA modules The FRA combines the measurement of data and its subsequent analysis The Installation and Diagnostics guide describes its installation The user should be familiar with MS Windows The FRA program consists of two distinct parts i e The user interface graphics and data analysis software The routines that perform all the communication with the Autolab instrument Familiarisation with FRA is best obtained by experimenting The on line help within the program provides most of the required help which may be nec
50. eee cese cee cseecseecseeeeeeeeeeeeeeeeeeeesecsecsaecsaecsaecseecseeeaeseeeseaeees 53 4 3 Time potential and current measurements 20 0 eee eee cee eeeeeeeeeeeceecesecssecsaecsaecsaecaaecaeeeseeeaeeeeeees 53 44 Time Ci 53 4 5 Single and Multiple Sine waves ueuuennesnnesnnesnessnensnensnnnnonnnnnnnnnnnnnnesnnesnnennnennnnsnonsnensensnensonnnnnnn 54 4 6 The measurement sequence isn sehe I SIE 54 4 7 Technical background cui era sr SI 55 4 8 Measurements using an Automatic mercury drop electrode nueesnesnesnnesnnesnensnensensnennennnnnnn 57 4 9 Sequence of measurements in case of synchronised measurements oocconccconnnonoconocononnnonnnonnninncnnnnnns 37 4 10 Measurements at open circuit potential oooonocnnnncnononocononcnnnnonnnannnnncnnncnno canon nono nooo conocio nn nonn crac crnnns 58 APPENDIX I FRA DATA FILES rsesossossnsossorsnsonsorsnsnnsorsnsnnorsnsnenarsnsnnsansesnesnrsnsnssnnsesnenassesnenansennen 59 4 User Manual FRA for Windows Version 4 9 APPENDIX IT BANDWIDTH AND GAING ssccsssssssessssessersesessersesessersesessessesessersessesessesessersees 61 APPENDIX III DEFINITION OF PROCEDURE PARAMETERS ursssssssssssnssossossnnsonsnnsnnsonenene 63 APPENDIX IV COMBINATION OF GPES AND FRA cccssssssssessssesserseseesersesesserseseeserseseeserseees 67 APPENDIX V NOISE CONSIDERATIONS sscsssssssssssssssessssessessesessesseseesesseseesessesecsessesesserseses 69 APPENDIX VI SPECIFI
51. el The Tau range factor is a special parameter which is default set to 1 It is related to the distribution of RC times in the circuits which are kept fixed during the fit In the K K fit is only done on the R value of each RC circuit The parameter should not be modified unless the theory as fully described in the article by B A Boukamp J Electrochem Soc 142 1885 1995 is understood The result of the test is the value of pseudo x the sum of squares of the relative residuals In each case the X for the real and the imaginary part is reported overall Y is a sum of real and imaginary x Large X value means bad fit small value good fit What is actually large and small depends on the number and the value of data points As a rule of thumb values lower than 10 usually mean an excellent fit reasonable between 10 and 10 marginal between 10 and 10 and bad for even higher values Moreover the residuals should be small and randomly distributed around zero The test can be carried out on real part imaginary part or both part of admittance impedance complex fit In the case of fit on one part only the second part of the measured data set is generated using Kramers Kronig transformation on the assumption that the system obeys K K criteria and then X for the second part is computed Definitions of pseudo Y 2 2 N Zre i Zre n Zimi Zim 125 Zef p 2 2 01 pZmZuloi Zlw
52. elected current must be between FACTOR1 current range and FACTOR2 current range The default values for FACTOR1 and FACTOR are 0 2 and 5 Thus a current range of 1 mA is selected for impedance s between 200 ohm and 5000 ohm The selected current range depends on the applied frequency This is due to the fact that lower current ranges have a lower bandwidth See Appendix The filter is set to a cut off frequency of the frequency to be measured multiplied by a user specified factor In case a multiple sine is applied the cut off frequency equals the highest frequency to be measured multiplied by this user specified multiplication factor However the highest cut off frequency is limited to 140 kHz FRA or 160 kHz FRA2 However with the FRA2 modules a fixed filter is used when the applied frequency is higher than 19 kHz The lowest applied cut off frequency is limited by software The default frequency limit is 10 Hz A cut off frequency close to the applied frequency factor for filter frequency close to unity cause significant attenuation of the signal as well as a severe phase shift Since both filters do not exactly match a systematic error will be found A reasonable minimum value for this filter factor is 32 The conversion rate of the two simultaneous sampling ADC s is set This is done by using the same crystal as used for the 16 bit DAC and by dividing its frequency by an integer number The default number of points for one cyc
53. ell and will influence the measurements Pre treatment The pre treatment facility allows conditioning of the electrochemical cell at specified potentials or currents during a specified time This pre treatment can be performed before each applied ac frequency or before each new applied dc potential or current If this facility is not to be used specify all times as zero Edit frequencies The frequencies can be edited from a separate window which can be opened by clicking on Edit frequency option just below the top window bar The frequencies to be applied can be calculated according to the parameters in the Parameter panel The exact applied frequencies and their amplitude can be changed in the second input screen A complete frequency scan can be divided in up to five sub scans This facility makes it possible to measure for instance from 50 kHz down up to 10 Hz with an amplitude of 0 005 V first and after that from 10 Hz down to 1 mHz at 0 05 V Begin and end frequency The sub scan is performed from the begin to the end frequency It is strongly advised to perform a frequency scan from high to low frequencies The frequency limits are 50 kHz down to 0 1 mHz FRA or 1 MHz down to 0 01 mHz FRA2 Number of points The number of frequencies in the sub scan Frequency distribution The distribution of the frequencies from the begin to the end frequency can be either linear square root linear or logarithmic The amplitu
54. ement Procedure name in Data presentation displays filename and path of the result file in graph Trigger Under this item the option Trigger is present After selecting this option the following window appears In this window the trigger pulse can be configured After enabling the trigger pulse option the Start button has to be clicked The program will go through pretreatment and equilibration and will then wait for the trigger signal 26 User Manual FRA for Windows Version 4 9 pretreatment equilibration measurement end of measurement 1 high A O SEN low Fig lla The Trigger option window Trigger option l Trigger option Enable trigger pulse option 8 Start measurement on input trigger TTL The trigger pulse can be a change from low to high or from high to low It should last at least 1 ms React on Abort Advance button during wait for trigger The trigger pulse should last at least 10 ms O Give output trigger TTL The trigger is given after pretreatment and equilibration at the start of the measurement Immediately after the measurement the output is set as before the measurement O Output from low to high Output from high to low DIO connections Use pin number 1 8 1 Pin 25 is the digital return lead of the Autolab Use port P1 of P20 Please note that there is a risk of introducing a ground loop when connecting an external instrument to Autolab This results in
55. entation window and allows merging of previously measured data with the current data Save work data Allows saving of edited or merged data as previously discussed Merge This option allows merging of two frequency scans at single potential or current The merged scans can subsequently be stored on disk using the Save work data option However conflicts may occur in the procedure parameters of the two merged data files The procedure parameters of the already loaded data are dominant This option is useful to obtain a full frequency scan from two or more separately measured scans For example in order to save time the low frequency part of a scan 1s measured using the multi sine mode and the high frequency part is measured using the single sine mode After a subsequent merge a full scan is obtained View The View option makes it possible to inspect one or more graphical presentations of the measured impedance data A maximum of 4 plot windows can be opened at the same time When the measurements are performed at one single potential or current a selection can be made from the following items Z versus Z Draw a plot of the quadrature impedance versus in phase impedance Y versus Y Draw a plot of the quadrature admittance versus in phase admittance Bode plot Draw a plot of the logarithm of the impedance and the phase angle versus the logarithm of the frequency Chapter 3 The FRA windows 37 Z Z versus f Draw in ph
56. equencies when the measurement time should be as short as possible Base frequency The lowest applied frequency in case the multi sine mode is used The applied signal is a super imposition the specified base frequency and 4 or 14 higher harmonics Cell off after measurement When a measurement is completed the cell can either be switched off or left switched on at a potential or current specified as standby potential Comments A panel to type in several lines of text Current range Current range to be used for galvanostatic experiments Define potentials w r t OCP The potential values specified under Potential on page 1 are applied with respect to the open circuit potential which is measured before the impedance measurements are started If the measurements have to be done at the open circuit potential the value to be specified is 0 000V Note that the potentials given under pre treatment and as stand by potential are not applied versus the open circuit potential Duration of measurement The total time the execution of the measurement should last including the equilibration time in case a potentiostatic or galvanostatic time scan is made Enable internal ac input of PGSTAT Enable internal ac input of PGSTAT If external inputs are used the DSG signal is also applied to the PGSTAT End potential or current The last potential or current of a potential or current scan This input is only requested for the potential
57. essary to perform the measurements and the data analysis This manual concentrates more on explaining the general concepts and backgrounds than on guiding the user through the program Moreover this manual tries to explain the possibilities of FRA Please keep this manual together with the Installation and Diagnostics guide The latter guide explains the installation 1 2 The concept The FRA screen consists of several windows one for manual control over the potentiostat galvanostat one for data presentation and manipulation one for entering the experiment parameters one for viewing the FRA settings and one for controlling the FRA modules Surrounding windows menu options and tool bars give extra facilities like cell diagnosis accessory control Autolab configuration access and data transfer to programs like Excel and MS Word The MS Windows related terminology used in this manual is in agreement with the standard as described in the book The GUI Guide international terminology for Windows Interface Microsoft Press Washington ISBN 1 55615 538 7 User Manual FRA for Windows Version 4 9 The following mouse conventions are used Quickly pressing and releasing the mouse button is called clicking A click of the left mouse button on a menu option a button an input item on the screen etcetera will result in an action Clicking and holding down the left mouse button is called dragging and is used for several purposes Y
58. esult will be One cycle is the minimum Number of cycles to reach steady state The period between applying the ac signal and start of the measurements This time is often needed to measure stationary state behaviour A standard value can be 10 Maximum time to reach steady state The maximum time between applying the ac signal and the measurements When the applied frequency is low the time of the specified number of cycles to reach steady state can be too high As soon as the previous criterion or this criterion is found to be true the measurement starts With a minimum fraction of cycle In case the Maximum time to reach steady state is shorter than the time equivalent to the duration of the minimum fraction of cycle the latter value is used to wait for steady state Chapter 3 The FRA windows 35 The effective time to wait for steady state now depends on four parameters f frequency Number of cycles to reach steady state neycles Maximum time to reach steady state tmax with a minimum fraction of a cycle Xtraction The time to wait for steady state twait 18 twait Neycles f if twait 2 tmax then twait Imax if twait 2 tinax then if twait lt X fraction fthen twait X fraction f These parameters are also stored as part of the measurement procedure so they might change when a procedure is loaded from disk In the panel below the results of the measurement can be observed after the Measure but
59. ette setup window gives the possibility to define the connected burette Please consult the manual of your burette for the parameters The Maximum time to check for Ready is the maximum time for the software waiting to receive a ready signal from the burette The DIO port used is shown on your Autolab front The Dose button will dose the amount specified above The dosed volume is displayed The Dose on button will dose with the speed displayed above The Reset button will give a reset command to the burette and sets the dosed volume to zero RDE control In order to control an external Rotating Disk Electrode RDE an option is available in the Utilities menu of the GPES manager In the hardware configuration an external RDE should be specified After selecting the RDE control item the following window appears 24 User Manual FRA for Windows Version 4 9 Fig 9 The RDE control window w RDE control Rotation speed r p m 1020 0 r p m 106 814 rad s Setup gt gt Close With the scroll bar it is possible to control the rotation speed of the RDE You can also enter the number of rotations per second by changing the r p m edit field or enter the rotation speed in rad per second in the rad s edit field After pressing the Setup button the RDE setup window appears Fig 10 The RDE setup window m RDE Setup RPM per Volt boo Maximum rotation speed 3000 DAC channel 3 or 4 3 Warning
60. he frequency domain clearly shows high amplitudes for the applied frequencies The horizontal axis is an arbitrary time scale 3 2 Status bar The lowest part of the screen is reserved for the status bar The Start button starts the execution of a measurement procedure After clicking this button other buttons appear which make it possible to advance to a next stage or to abort a measurement procedure The Status and Message panel give important control information A measurement can be temporarily suspended by pressing the lt Hold gt button More information on the sequence of events after starting the measurements is given in a separate chapter 3 3 Autolab manual control window The Manual control window gives full control over the potentiostat galvanostat of the Autolab instrument Note that some of the presented Autolab settings are part of the measurement procedure The Manual control window consists of several panels Fig 13 Autolab manual control window fm Manual control Current range Settings Potential iR compensation see Il o ri on 4 mM 2 F 100 mA High Sens off 000 y 00 O i 10 mA O X1mA High Speed O RX 100 uA Current O i 10uA Potentiostatic si Potential 1 u Pe 100 nA F 10nA Time Potential Current range In the Current range panel the green LED indicates the actual current range A mark in the neighbouring che
61. his error appeared error 1 Not enough memory There is not enough memory to carry out fit or simulation Try to free some memory by closing other applications Appendix VIII Fit and Simulation 85 error 2 Overflow in numerical calculations Value of parameters are so large or so small that overflow appears in numerical calculations Check the values of element parameters and change them or use constraints to more moderate values error 51 GAUSSJ Singular Matrix 1 Two or more parameters are dependent or nearly dependent This error can also happen if some parameters have extreme values Consider use of another CDC change parameters to more moderated values or use constraints error 51 GAUSSJ Singular Matrix 2 Two or more parameters are dependent or nearly dependent This error can also occur if some parameters have extreme values Consider using another CDC change parameters to more moderated values or use constraints error 60 error in CDC The entered CDC is not correct Appendix IX Kramers Kronig test 87 Appendix IX Kramers Kronig test The Kramers Kronig test The Kramers Kronig K K test can be used to check whether the measured system is stable in time and linear Stability and linearity are a prerequisite for fitting equivalent circuits If the system changes in time the data points measured on the beginning of the experiment do not agree with those measured at the end of the experiment Stability problems are most
62. ial of 50 normally found at an amplitude of 15 mV rms A resolution of 0 5 is observed for a measurement of an impedance of 100 000 ohm when the current range is 1 mA Conclusion A minimum resolution of 0 5 is required if the maximum impedance error should be better than 1 A higher accuracy than 0 2 requires a minimum resolution of 1 Appendix VIII Fit and Simulation 79 Appendix VIII Fit and Simulation The Fit and Simulation option in the program allows you to simulate responses of equivalent circuit and to fit the circuit parameters to the measured data using the non linear least squares method The equivalent circuits can be defined by the user using Circuit Description Code It is possible to define elements with fixed values as well as constraints for values of fitted parameters This option is based on the work of Dr B A Boukamp as first published in Solid State Ionics 20 1986 31 44 and coded in the program EQUIVCRT by the same author Circuit description code cdc This is a code used for defining equivalent circuits It consists of letters representing circuit elements and round and square brackets representing parallel or serial arrangement of elements The table below shows the meaning of the letters letter element letter element R resistance Q constant phase element CPE C capacitance T hyperbolic tangent element L inductance O hyperbolic cotangent element W Warburg impedance G Gerischer impedance S
63. ift 0 When the frequency of the noise is fo as well the amplitude of the current signal will be doubled This yields an impedance of 500 ohm Fig 23 Effect of noise with frequency f on the impedance measured at frequency fo The noise amplitude is equal to the amplitude of the frequency of interest f Data presentation File Copy Plot Analysis Edit data Noise rejection for different number of integration cycles E 000 QG 00 Conclusion A longer integration time will improve the result of the measurements Appendix VII Theoretical considerations on the performance of FRA instrument 77 Effect of non stationary dc current Impedance measurements with a non stationary dc current are simulated by performing FFT calculations on a pure sine wave for the potential and sine wave with super imposed dc slope for the current The error in the calculated impedance Z as a function of the dc component of the current has been investigated In the simulation calculation it is assumed that the current range is 1 mA and the real impedance is 1 000 ohm Fig 24 Effect of non stationary dc current on calculated impedance Data presentation File Copy Plot Analysis Edit data Effect of change in dc current on impedance measurement 0 250 0 500 0 750 Rel ative change in dc current see text E 000 Q 00 x is the relative change in de current x 0 corresponds to a perfect stationary current
64. is calculated assuming that a resistance Rs is in series with a capacitor Cp Select frequency The impedance admittance plots can be drawn at one or more frequencies A window appears from which one or more frequencies can be selected or deselected The potential scans measured at the frequencies will be shown The data measured at the selected frequencies are plotted in different colours in one or more of the plot available types The frequency values at which the frequency scans are displayed are shown in a drop down menu in the upper left corner of each graphical window The value selected from the drop down menu is the so called work data set All Edit and Analysis action are performed on this data set A maximum of four plot types can be displayed at the same time Each plot in a separate window When a time scan has been performed one or more of the following time scan plots can be selected Z versus t Draw a plot of the in phase impedance versus time Z versus t Draw a plot of the quadrature impedance versus time Y versus t Draw a plot of the in phase admittance versus time Y versus t Draw a plot of the quadrature admittance versus time Cs versus t Draw a plot of the substituted serial capacitance versus time Z versus t Draw a plot of the in phase impedance 27f versus time Z versus t Draw a plot of the quadrature impedance 27f versus time Z Z versus t Draw in phase and quadrature imp
65. le of ADC s equals 1024 For lower frequencies the FRA2 also measures 2048 or 4096 points per sine wave At frequencies higher than 200 Hz FRA or 488 Hz FRA2 more than one sine wave is measured with 1024 points The oscilloscope windows will show more than one sine wave Each memory location is 24 bits wide Since the ADC s are 12 bits the maximum number of conversions per memory location equals 4096 Thus a frequency of for instance 200 Hz is sampled with 200 kHz conversion rate Measurement of one cycle takes 1 200 s 0 005 s Up to 4096 cycles can be measured and averaged The maximum time of measurement or integration time equals 1 200 Hz x 4096 20 s When the frequency of the applied sine wave is so low that the time between two samples of the ADC allows more than one conversion per point multiple conversions are added within the same memory location So the conversion rate of the ADC is always as high as possible in order to perform as many measurements as possible The actual integration will never be shorter than the specified integration time and the time needed to complete the specified minimum number of integration cycles see FRA manual control window Chapter 4 Measurements 57 During conversions the software checks the overload indicators As soon as an overload is detected the measurement is aborted the gain of the corresponding amplifier is lowered and the measurement is performed again 6 After completing the
66. lected from a neighbouring window The Print Preview button allows you to preview the print out of data Print setup This option gives access to the standard window for printer setup and control Load data The Load data option allows load of previously measured data from disk It is also possible to load data files from the DOS version of FRA If this is required click the List Files of Type drop down button and select the proper option Save data Store the most recent measured data under the current procedure name on disk The data are stored in the so called data directory together with the corresponding procedure parameters Save data as The Save data as option is similar to the previous option but the name of the file name containing the data can be specified Convert to ASCII This option allows conversion of the FRA data files to readable ASCII files These files can be read by any spreadsheet program but also by third party data analysis programs Chapter3 The FRA windows 21 Fig 8a Convert data Convert data Save data as File info f Z 2 tm Ede Ide EQUIVCRT frademo O f Y Y Cs tm Ede Ide OE Z 2 tm Ede Ide OE Y Y Cs tm Ede Ide O Mott Schott y PX Include tm Ede and Ide Feri ferro Output filename First a FRA output data file has to be selected After clicking on a file in the list box some file info is given To proceed the
67. llaneous Load procedure FRATEST from the testdata directory Procedure Open c 4MUTOLABATESTDATAAFRATEST Start execution of the procedure Procedure Start Parameter Store the data in the file FRAQUT in the data directory a DataSet Saveds c AUTOLABSDATA FRAQUT Information Give a beep System Beep Print the measurement procedure Print Procedure Insert comment Syntax i lt comment gt om OK Cancel A Every project command can be inserted in the project deleted or moved to another place A short description of the command is given in the information and syntax box 30 User Manual FRA for Windows Version 4 9 Using the parameter button one can define the parameters that belong to that specific command Project example Example 1 Record frequency scan on all available MUX channels This example script will record a frequency scan on all available MUX channels and store the results automatically as fra scanner test_001 fra scanner test_002 etc until the last available channel is reached Procedure Open c autolab testdata fratest ForAllChannels c autolab data fra scanner test_ Window The Window option allows selection of windows which should be shown on the screen The Tile option gives the default partitioning of the screen The Close all option will delete all the FRA windows except for the status bar and the FRA Manager window Help The Help option is
68. lue using the slider in the Frequency panel 12 Click Measure again 13 At the end click Stop and close the FRA manual control window 2 3 Data manipulation with FRADEMO 1 Click the File option in the upper left corner of the screen 2 Click Load data 3 Type AUTOLAB testdata frademo dfr Press ENTER 4 Click the upper right button of the Data presentation window The Data presentation window will fill almost the whole screen 5 Click the View option Select Z versus Z 6 Click now the upper right button of the Z versus Z window The Z versus Z plot will now fill almost the whole screen It is also possible to drag the borders of the window in such a way that the window is maximised or that the window looks like a square Now you should see a semi circle which at the right side becomes a straight rising line 7 Click Analysis on the Data presentation window Select the Linear regression option Chapter 2 Getting started with FRA 15 Fig 5 Straight line analysis Frequency Response nalyser Eile Method Utilities Options Project Window Help Method Potentinctatic tron Linear regression Results Slope 9 954E 1 begin 6 173E 2 s d 1 08E 2 Y begin 2749E 2 Len peri 9 Intercept s d 8 09E 0 end 6 173E 2 Chi square 3 572E 1 Y end 5 512E 2 Corr coeff 9 997E 1 YiatX 0 3 392E 2 No points X atY 0 3 407E 2 Set line Status Messages
69. measurement the data from the memory of the two ADC s are read by the computer A Fast Fourier Transform method is applied to calculate the frequency spectra of both potential and current These spectra are used to calculate the in phase and quadrature components of the impedance The software allows the user to view the data read from the memory the time domain plot as well as the FFT processed signal the frequency domain plot For more information about the basics of the approach of this instrument see R J Schwall A M Bond R J Loyd J G Larsen and D E Smith Analytical Chemistry Vol 49 no 12 October 1977 p 1797 1805 and p 1805 1812 4 8 Measurements using an Automatic mercury drop electrode The Autolab instrument supports several mercury drop electrode configurations The IME or IME663 interface for mercury drop electrode provides an interface The FRA measurements can be done at a static as well as at a mercury drop electrode A new drop is created when New drop has been checked on page 2 of the Edit procedure window and the presence of an automatic electrode is indicated in the hardware configuration In the sequence of events a new drop is created just after the first conditioning potential or current stage has finished if any In the Edit screen called Pre treatment Yes is specified behind New drop Second conditioning time is greater than zero This means that a new drop is created at this Seco
70. mum and maximum Y value s with their corresponding X values Interpolate The Interpolate option allows to calculate one or more X values or Y values which correspond to a given value on the axis A linear interpolation is used to calculate intermediate values Data info this option sets a marker in the presently loaded curve and gives the corresponding frequency and X Y values The Kramers Kronig K K test This test can be used to check whether the measured data comply with the assumptions of Kramers Kronig transformation These assumptions are 1 the response is only related to the excitation signal 2 the response is linear or the perturbation is small e g lt 10 mV for non linear systems 3 the system does not change with time and 4 the system is finite for all values of including zero and infinity If the investigated system changes with time due to e g ageing temperature change non equilibrium initial state etc the test fails Failure of K K test usually means that no good fit can be obtained using the equivalent circuits method This option is based on the work of Dr B A Boukamp as published in J Electrochem Soc Vol 142 6 June 1995 and coded in the program RCNTRANS by the same author Please refer to the Appendix for more information about this option Chapter 3 The FRA windows 45 Fit and Simulation This option allows you to simulate responses of equivalent circuit and to fit the circuit parameters
71. n CDC located at the top A list of parameters of CDC elements and a panel for parameter editing are located at the middle of the window The Fit panel and buttons for starting and stopping fit and simulation are located at the bottom of the window The functions of these components are described below File menu Load circuit Loads the previously saved user defined equivalent circuit from the disk Save circuit Saves the currently used equivalent circuit to the disk Copy to work data The most recent calculated data which result either from a simulation or from the fit are turned into the so called work data and thus remain available after closing the Fit and simulation window Normally the fitted and simulated data sets are erased The work data can be stored on disk using the File option on the Data presentation window Appendix VIII Fit and Simulation 81 Close Closes the window and returns the focus back to the Data presentation window The simulated and fitted data sets are lost unless Copy to work data is used Results of fitting are printed in the Analysis results window Edit menu Circuit Description Opens a window for entering or editing the Circuit Description Code CDC The CDC can be modified and also standard circuits can be inserted using the Insert circuit command in the toolbar If the code contains syntax errors like bracket mismatch it will not be accepted The Help button displays a list of av
72. n of the normalised frequency Data presentation File Copy Plot Analysis Edit data Noise rejection for different number of integration cycles Transfer function 76 User Manual FRA for Windows Version 4 9 The transfer function 1 e the impedance normalised with respect to f fo 1s calculated for a different number of integration cycles In case of e g 100 Hz an integration time of 0 01 s gives one integration cycle The default integration time of 1 s gives 100 integration cycles The transfer function resembles the calculated curve for a different FRA instrument based on correlation with synchronous reference signals Ref Impedance Spectroscopy by J Ross Macdonald Ed Wiley New York 1987 Conclusion It is clearly shown that a larger number of integration cycles and thus a longer integration time significantly improves noise rejection Effect of noise on impedance measurements The effect of noise on impedance measurements can also be simulated This is done by adding noise with frequency f to a signal of interest at frequency fo The calculations are done using a sine wave for the potential and the current Both have the same amplitude and frequency fo A sine wave with the same amplitude but different frequency f is superimposed on the potential and current perturbations The simulation is performed assuming a current range of 1 mA The perfect impedance should therefore be 1 000 kOhm and the phase sh
73. n the program is exited in a regular way Default graphical settings All parameters which determine the presentation of the graph will be set to their default i e as they were when the graphical settings were saved the last time Chapter 3 The FRA windows 43 Fig 15 Two potential scan plots amp Data presentation Eile View Copy Plot Analysis Editdata Window EZ versus E _Iolx Bz Cs versus E are are Mercury electrode 1 Mercury electrode Analysis The analysis menu has four options Selection of these options opens a specific window to perform the operation and to display the results The results are printed in the Analysis results window as well This window can be made visible from the Window option on the FRA manager menu bar Linear regression The Linear regression option makes it possible to fit a straight line through a part of the measured curve When the option is selected two windows appear One is the Linear regression window and the other is the Markers window When the begin and end point of the line have been marked on the measured curve and the OK button on the Markers window has been clicked a line is drawn in such a way that the sum of squares of the differences between measured data points and calculated line is minimum The slope of the line dY dX the intercepts i e Y at X 0 and X at Y 0 and several other helpful data are given More lines can be fitted when the
74. nce plot Select File from the upper left corner and select Save data as Enter a filename and make sure that the Directory is Autolab DATA and press OK Now select File again and click Convert to ASCII Select the data file created above and click Convert Select the required file format and click Convert again The data are stored as an ASCII file with the specified format For explanation of File extensions see Appendix 1 If a potential scan is loaded a potential value should be selected before the file can be converted For each potential a file is created with an extension as explained in Appendix 1 Click in the upper left corner of the screen and exit the Frequency Response Analyser program Chapter3 The FRA windows 19 3 The FRA windows 3 1 FRA Manager window The title bar of the FRA Manager window contains several options i e File Method Utilities Project Window Help File menu This menu contains options that are usually present in Windows programs Fig 8 The File menu la Frequency Response Analyser Utilities Options Project Window Help Cti 0 f Method Potentiostatic freq scan Procedure Frademo Ctrl S Save procedure As Print Ctrl P Print setup Load data Save data Save data As Convert to ASCII Load Calibration file Delete files Exit arm ee Crea BN Start Il E 7 amp amp inbox Out Tasks Mic BY Microsoft W GjEspoing P E Fre
75. nd conditioning potential after which the specified conditioning time is included If Repeat pre treatment before every frequency is Yes then every measurement is performed at a new drop In case it is No but Yes is specified for Repeat pre treatment before every potential a new drop is created for each frequency scan at a new dc potential or dc current 4 9 Sequence of measurements in case of synchronised measurements The sequence of measurements in case of synchronised measurements is as follows 1 If the duration of the first conditioning potential or current is larger than zero the first conditioning potential or current is applied 2 If New drop is checked on Page 2 of the Edit procedure window New drop signals are generated 3 If the duration of the second conditioning potential or current is larger than zero the second conditioning potential or current is applied 58 User Manual FRA for Windows Version 4 9 4 If the duration of the third conditioning potential or current is larger than zero the third conditioning potential or current is applied 5 The measurement potential or current is applied 6 The equilibration period starts with the ac signal applied and the instrument settings are controlled 7 Immediately perform the measurements without controlling the settings This assures accurate timed or synchronised measurements after applying the dc potential or current 8 If the measuremen
76. ndow are called work data and can be stored from the File menu of the Data presentation window in a work data file This file cannot be distinguished from the files with measured data Both types of files have the same format and layout On the message line at the bottom of the graphical display important text about the required user actions during analysis of editing data appears If no message is displayed the currently measured potential and current are displayed 36 User Manual FRA for Windows Version 4 9 Copy The Copy option allows to copy the graph to clipboard or to dump the graph in a bitmap file BMP or a Windows meta file WMEF These files can be read by programs like Paintbrush Excel or MS Word These programs allow editing of the graphs Please note that the size of the axis annotations etc in the meta file depend on the size of the Data presentation window Moreover the sizes in the meta file may be somewhat different from what is displayed in the Data presentation window The best way to copy the graph to MS Word is to make a W MF file using the Copy to option The best result is obtained by doing this from a maximised Data presentation window By default FRA only draws dots It is sometimes better to draw lines This can be achieved by double clicking the data points in the graph For further information see the paragraph on Editing graphical items File The File option allows saving the data presented in the Data pres
77. ns in both programs When a measurement procedure is being executed user interaction with the programs should be avoided Apart from GPES and FRA no other application should be active Appendix V Noise considerations 69 Appendix V Noise considerations Some rules for preventing excessive noise are Do not use unshielded cables and connections Place the electrochemical cell as far as possible from electrical appliances Place the cell inside a faraday cage The Differential Electrometer Amplifier increases the noise Do not use it if it is not required i e a two or three and not four electrode cell is used and the dc current does not exceed approximately 10 to 50 mA Use the high stability mode where possible Appendix VI Specifications maximum output current maximum output voltage potentiostat galvanostat potential range applied potential accuracy applied potential resolution measured potential resolution current ranges applied and measured current accuracy applied current resolution measured current resolution at current range of 10nA potentiostat bandwidth 1 potentiostat risetime falltime 1 V step 10 90 1 potentiostat modes input impedance of electrometer input bias current 25 C bandwidth of electrometer IR compensation resolution four electrode control front panel meter Analog outputs BNC connector control voltage input multichannel option pAutolab type IIT FRA
78. nterrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes multipleWE option Autolab with PGSTAT100 250 mA 100 V yes yes 10V 0 2 of setting 2 mV 150 uV 300 or 30 uV 10 nA to 100 mA in eight ranges 0 2 of current and 0 2 of current range 0 015 of current range 0 0003 of current range 30 fA 500 kHz lt 500 ns high speed high stability gt 100 GQ lt 8 pF lt 1pA gt 4 MHz depending on selected range 0Q 200Q at 100 mA range to 0Q 200 MQ at 10 nA range current interrupt and positive feedback available 0 025 yes potential and current potential current and optionally charge yes no 72 User Manual booster option analog integrator time constants interfacing A D converter auxiliary input channels D A converter auxiliary output channel digital I O lines WxDxH weight power requirements FRA for Windows HAutolab type III FRA2 no yes 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 1 16 bit three channels 1 48 26 x 26 x 10 cm3 4 2kg FRA2 144 W 100 240 V 50 60 Hz Version 4 9 Autolab with PGSTAT12 no optionally available 10 and 100 ms land 10s USB 16 bit with software programmable gains of 1 10 and 100 2 16 bit four channels optionally eight 1 48 52 x 42 x 17 cm3 18 kg 247
79. od Potentiostatic freq scan Procedure FRATEST FRA manual control EJ Manual control Current range Settings Potential 7 iR compensation Range Oia cn a Ki O 2 10 100 1 10 100 1 10100 1 10 aa 1 10 F 100mA HHz mHz Hz kHz MHz BE10mA High Sens at i 00 Frequency Amplitude O RK 1mA High Speed Al gt duo gt Of 100uA Current O i 10uA Potentiostatic A O Potential 10 00 kHz 01002 Y A E A O miona eit One O Time j FRA settings Potential iR comp Off Integration time s Minimum number of cycles to integrate Number of cycles to reach steady state r Y y Offset potential current Maximum time to reach steady state s Yv with a minimum fraction of a cycle Ede Use external inputs P E ac ide Results Rs freq Cs Measure z Title and Subtitle I RA test procedure with dummy cell connect WEICH 4 gt 500 71 hr Status Messages A Start EJesitproced E Frequency R J 1 Data present U Manual contr B screen Capt Cl FRA settin FRA manual Sy 3 21 PM FRA manual control 9 Click the greenish buttons on the toolbar to activate Oscilloscope windows 10 Click the Stop button on the FRA manual control window 1 Change the frequency to a lower va
80. of electrochemical impedance spectroscopy We would like to refer to some excellent textbooks C M A Brett and A M O Oliveira Brett Electrochemistry Oxford science publications ISBN 0 19 855388 9 Allen J Bard and Larry R Faulkner Electrochemical Methods Fundamentals and Applications J Wiley amp Sons ISBN 0 471 05542 5 R Greef R Peat L M Peter D Pletcher and J Robinson Instrumental Methods in Electrochemistry Ellis Horwood Limited ISBN 0 13 472093 8 John R Scully David C Silverman and Martin W Kendig Electrochemical Impedance Analysis and Interpretation STP 1188 ASTM ISBN 0 8031 1861 9 1 3 The instrument and hardware description The FRA hardware consists of a digital signal generator DSG a signal conditioning unit SCU and a fast analog to digital converter with two channels ADC The DSG consists of a large digital memory which is loaded with the digital representation of the applied signal and a fast settling 16 bit digital to analog converter A multiplying digital to analog converter controls the signal amplitude This architecture ensures accurate signal generation The time dependent potential and current signals from the potentiostat are filtered and amplified by the SCU and recorded by means of the ADC The acquired signals are stored in the digital memory on the ADC board This digital memory allows time domain averaging of up to 4096 repetitive measurement cycles Each cycle can consist of 4096
81. olution of dual channel ADC 1 in 4096 12 bits ADC input ranges 0 01 V to5 V 10 ranges software programmable Software specifications maximum number of frequencies maximum number of dc potentials or de currents measurement modes e automatic current ranging e Ist 2nd and 3rd conditioning time e Ist 2nd and 3rd conditioning potential e or conditioning current wait time before measurement e stand by potential e stand by current e potential scan measurement initial and final potential e current scan measurement initial and final current e time scan measurement end time interval time integration time minimum number of cycles to be integrated minimum number of cycles to reach steady state maximum time to reach steady state e With a minimum fraction of cycle e repeat prepolarisation before each frequency scan e repeat prepolarisation before each frequency e synchronised measurement e cell off after measurement e potentials with respect to open circuit potential Appendix VI Specifications 73 20000 not checked single sine 5 superimposed sines within one decade 15 superimposed sines within two decades optional mode 0 30000 s 10V 1 A PGSTAT12 20 30 100 or 50 mA PGSTAT10 0 30000 s 10V 1 A PGSTAT12 20 30 100 or 50 mA PGSTAT10 5V 1 A PGSTAT12 20 30 100 or 50 mA PGSTAT10 1 30000 s 1 30000 s 0 1 10000 s 1 16 0 30000 0 30000 s
82. open a sub window to enter the CDC manually 6 Either type in the circuit code or insert one of standard predefined circuits The predefined circuit is inserted at the cursor position so they can be combined with user defined circuits 7 Press OK in the sub window to return to the Fit and Simulation window The CDC is now displayed in the Circuit description panel each element having an ordinal number added to the element s symbol 8 Select elements one by one in the element list appearing below the Circuit description panel Enter the value of the parameter 9 Choose whether the simulation should take place in impedance or admittance representation the displayed result is always in the same representation as the displayed data set Element parameters are defined independently of the actual representation used 10 Press Simulate button 11 If the simulation is finished you may want to save the used CDC To do this use option Save circuit option from File menu Fit and Simulation window 12 If you want to use or save simulation results choose option Copy to work data File menu Fit and Simulation window to replace the actual data set with the simulated data 13 Finish simulation by pressing Close button Fit and simulation error messages error 1 xxxx Internal error of the fit and simulation module String xxxx contains specific information about the problem Please report xxxx and the circumstances under which t
83. option from the File menu can be used to save the adjusted data set Element subtraction The influence of a circuit elements can be subtracted from the measured data This can simplify the analysis of the data All elements which can be used in the Fit and simulation option can also be subtracted The element can either be subtracted from impedance data or from admittance data The impedance data should be used in case the element is supposed to be in series with the remaining circuit the admittance data should be used if the element is parallel with the remaining circuit A description of the available circuit elements can be found in the appendix on Fit and simulation Dispersion functions for elements The table below defines the dispersion functions for the elements in both impedance and admittance representation 27f 46 User Manual FRA for Windows Version 4 9 CDC element impedance admittance parameters R resistance R 1 R R C capacitance j C JOC C L inductance JOL j KoL L W Warburg 1 Y jw Y jo Y impedance Q constant phase Y jo Y jo Y n element T hyperbolic y 50 coth Bjo Kio tant BJjo Y gt 8 tangent element O hyperbolic x 50 tanhl 8 50 Y 50 com B j0 Y 8 cotangent element G Gerischer y K jo Y K j Y K impedance Please note that the definition of the Q element differs from the EQUIVCRT program Chapter 3 The FRA windows 47 fig 16b The marked points have been rem
84. ory press the Fit button again you can also increase the maximum number of iterations selecting Fit control parameters in Edit menu of Fit and Simulation window in order to continue with fitting 11 You may wish to change the fit settings Edit menu Fit and Simulation window to fine tune the fitting process Or select points for fit Select frequencies in Option menu Fit and Simulation window 12 Fit results are automatically copied to Analysis window 13 Should an error message appear consult the section on error conditions 84 User Manual FRA for Windows Version 4 9 14 If the fit is finished you may want to save the used CDC To do this use the Save circuit option from the File menu Fit and Simulation window 15 If you want to use or save fitted data set choose the option Copy to work data File menu Fit and Simulation window to replace the actual data set with the fitted data 16 Finish fitting by pressing Close button Simulation of equivalent circuit response 1 Load the data file FRADEMO from the AUTOLAB TESTDATA directory 2 Choose Fit and Simulation from Analysis menu Data presentation window 3 Make sure that the switch Fit Simulation bottom part of the window is in Simulation position 4 Open the File menu on the Fit and Simulation window Load the Circuit Description Code file FRADEMO from the AUTOLAB TESTDATA directory This circuit will fit rather well 5 Click the Circuit Description panel to
85. ot types can be edited After clicking OK all future plots will appear with the updated axis text The modified axis description will be stored on disk when the FRA program has been exited in a regular way This options offers also the possibility to specify an Isotropic plot The plot will be shown isotropic the next time you open the plot Fig 14a Change axis text window Change axis text Name Horz axis Main vert axis 2nd vert Axis Isotropieplet Z ohm Z ohm Y mho logZIlo phase degl Z ohmlo Z ohm Z error o Z error Z ohm o Z ohml Z ohmlo Z ohml OA 42 User Manual FRA for Windows Version 4 9 Fig 14b Example of an Isotropic Z Z plot Data presentation Ed File View Copy Plot Analysis Editdata Window ba Z versus Z black zl FRA test procedure with dummy cell connect WE c 1 000K 0 0 100K 0 350K 0 600K 0 350K 1 100K zZ i ohm Save graphical settings The presentation of the graphs is determined by many parameters like the marker type of each displayed data set the format of the axis indices the colours etc All these parameters can be modified see below The modified settings can be saved by selecting this option Only one set of graphics parameters can be saved so any new plot type subsequently created will use the newly saved graphical settings as default The graphical settings are stored on disk whe
86. ou can focus on an item on the screen without an action You can drag a window when the mouse pointer is in its title bar It can be used to shrink or to enlarge a window when the mouse pointer is on the border of a window Finally you can drag a scroll bar a slider or a zoom panel A double click of the left mouse button is used to perform particular actions Except for the standard uses in window actions it is used to edit the graph in the Data presentation window A click of the right mouse button is used to open a zoom panel in the Data presentation window or to shrink or enlarge the Graphics panel in the Print menu window This panel appears after selecting Print from the File option in the FRA Manager window The following keyboard functions are supported RETURN ENTER key jump to next data input field select menu option or click button with focus left and right arrow key move cursor in data input field up and down arrow move up and down in a menu ALT puts focus on the menu bar of the window with the focus typing a subsequent underlined character will move the cursor to the corresponding menu item and a RETURN ENTER will select the menu item ESC aborts the execution of the measurement procedure Fl access Help F4 plot rescale FS starts the execution of the measurement procedure F6 and shift F6 change focus to the next window Chapter 1 Principles of operation 7 This manual does not describe the background
87. oved from the data set Frequency Response Analyser ol x Eile Method Utilities Options Project Window Help Method Potentiostatic freq scan Procedure FRATEST amp Data presentation x File View Copy Plot Analysis Editdata Window CEI m FRA test procedure with dummy cell connect WE c FRA test procedure with dummy cell connect WE c J 90000000000000000000000009 o 3 0 2 N o 2 Lied oo Bap aseyd log f Status Messages HA Start E Screen Capture Z Edit procedure E Frequency Res El Data present 1 Manual control Ey 3 54 PM Editing graphical items and viewing data Except for the available options items of the graph can be edited by double clicking them The following items can be double clicked the axis labels the axis itself the axis description the plot title and subtitle the data Colours sizes marker types text formats axis position all these things can be changed Please take some care with changes in Colours E g do not make the data colour the same as its background colour By double clicking the data points a window appears which among the standard graphical operations also gives the possibility to view the data values itself and to edit them Moreover the data can be copied to clipboard and subsequently be entered into e g a spreadsheet program The format of the data is similar to the forma
88. points This feature provides high accuracy and reproducibility Since a cycle can consist of 4096 points and a measurement can consist of 4096 repetitive cycles a single impedance measurement can take 4096 x 4096 AD conversions for each channel 8 User Manual FRA for Windows Version 4 9 Fig 1 Scheme of the FRA instrument dc input FILTER i ac input PGSTAT i output FILTERS AMPLIFIERS 12 bit E output ADC The analysis of the time domain measurements is done by means of the Fast Fourier Transform method Both the potential signal e t and current signal i t are transformed to E f I f and their complex conjugated E f and I f The cell impedance Z is calculated from the equation Z E f EH MIO ED The older FRA module allows measurements in the range of 0 1 mHz to 50 kHz The newer FRA2 module allows measurements in the range of 0 01 mHz to 1 Mhz The module can be used in two different modes single sine i e a signal with a single frequency is applied multiple sines i e a signal with more than one frequency is applied The single sine mode offers highest accuracy at higher frequencies e g higher than 50 Hz However at low frequencies the time of measurement of a complete frequency scan can cause a problem The multiple sines mode provides the opportunity of measuring 5 frequencies within one decade or even 15 frequencies within two decades in a single measurement cycle This method s
89. quare brackets mean that the elements enclosed in the brackets are arranged in series Elements enclosed in round brackets are arranged in parallel In order to simplify the notation it is assumed that if CDC starts with letter instead of a bracket the elements are arranged in series Therefore R CW and R CW are equivalent A number of examples of CDC together with the corresponding equivalent circuits are shown RCL RCL RRQ R CIRW R CIR CIRW DIQ Dispersion functions for elements The table below defines the dispersion functions for the elements in both impedance and admittance representation 27f 80 User Manual FRA for Windows Version 4 9 CDC element impedance admittance parameters R resistance R YR R C capacitance j C JOC C L inductance JOL j L L impedance Q constant phase 1 jo X jo Y n element T hyperbolic a Y B Y th By Y y jO tanh B jo 0 tangent element jo gt J 0 a dl O hyperbolic A z Y B Y tanh B Y y jO Jcoth B4 jo 0 cotangent jo an jo ovd J element G Gerischer y K jo Y JK jo K impedance Please note that the definition of the Q element differs from the EQUIVCRT program of Dr B A Boukamp Fit and simulation window When the Fit and Simulation window is opened the settings are similar to the previously closed window The window has a number of drop down menus and a panel for equivalent circuit descriptio
90. quenc A Microsoft us 390 AR SRR 17 53 Open procedure A procedure is a file containing all the experiment parameters It contains measurement parameters potentiostat galvanostat settings and graphics display values The extension of the file which is mentioned in the File name field should not be changed The directory in which the procedure file is stored is called the procedure directory When the directory in the Open procedure window is changed and a procedure file is successfully loaded from this new directory this new directory becomes the new default procedure directory 20 User Manual FRA for Windows Version 4 9 It is also possible to load procedure files from the DOS version of FRA If this is required click the List Files of Type drop down button and select the proper option Save procedure This option will save a procedure under its current name in the procedure directory Save procedure as The Save procedure option allows storage of a procedure on disk in the procedure directory with a different name as the current one Please use the default file extension as mentioned in File name field or omit the extension In the latter case the correct extension will be added Print The Print menu window appears The Print select panel makes it possible to choose between the print out of the measured data the experiment parameters or a dump of the data presentation window The type of data or the window can be se
91. rge off diagonal elements are present it suggests that the parameter corresponding to the row is not independent from the parameter corresponding to the column in the matrix Fitting does not give correct results if parameters are not independent The absolute value of elements of the covariance matrix depend on the way the weighing factors are defined Show residual plot Displays residual plot 1 e difference between the fitted and the measured data for both real and the imaginary part of impedance admittance Circuit description panel This panel displays the current Circuit Description Code CDC Each circuit element consist of a character describing its type and a digit to distinguish between elements of the same type To enter a new CDC or to modify the existing one it is necessary to click the panel to use Circuit description option of the Edit menu or to press control C The Edit circuit description window appears which allows to modify the CDC or paste one of standard CDC In this sub window only letters standing for elements and the brackets should be entered the digits are added automatically when the sub window is closed The Help button gives an overview of the codes and bracket uses The Insert circuit menu at the top of the sub window allows you to insert complete circuits List of CDC parameters The list at the middle part of the Fit and Simulation window shows symbols of elements as in the CDC string above a
92. ro Find Circle Circuit Rs Rp CPE Rs ohm 7 51293e 1 Rp ohm 3 14616e 2 CPE F 2 87564e 6 n 0 85937 Eind circle Status Messages FF Start E Edit procedure BB Frequency Respons 1 Data presentatio U Manual control 2 Screen Capture Ey 3 24 PM is Close the Z versus Z window 19 Click Plot and select Change axis text 20 Change for the Z versus Z plot the Horizontal axis and Main vertical axis text so that they indicate that electrode impedance is shown 21 Click View and select the Z versus Z Now the axis text has been changed 22 If the precision of the axis annotation is not sufficient double click the axis annotation and specify a new value for the precision and click OK 2 4 Measuring double layer capacitance as a function of potential 1 Click Window Select the Tile option 2 Click Method on the Title bar and select Potentiostatic Potential scan 3 Specify the next values in the Edit procedure screen Start potential V 0 V End potential V 1 V Step potential V 0 02 V 4 Connect the working electrode lead to WE d 5 Click Edit frequencies in the Edit procedure screen Chapter 2 Getting started with FRA 17 6 Specify Begin frequency 1000 Hz End frequency 100 Number of frequencies 3 Amplitude 005 V Select a logarithmic frequency distribution Fig 7 Double layer capacitance measurements amp Data presentation
93. scan method 64 User Manual FRA for Windows Version 4 9 Equilibration threshold level If enabled the Equilibration stage will be aborted after reaching this specified current The measurements will start as soon as this threshold is exceeded This option is not available for galvanostatic measurements Equilibration time Time between applying the dc potential or dc current and actual impedance measurement In case of synchronised measurements the minimum time is s First second and third conditioning potential or current Before the actual ac impedance measurement a conditioning potential or current can be applied When the duration is set to zero the stage is discarded Interval time The time between frequency scans of impedance measurements in case a potentiostatic or galvanostatic time scan is made The minimum interval time is at least two seconds but will depend on the minimum cycles to integrate and the maximum time to reach steady state see the FRA manual control window If the interval time is exceeded a message will be given but the measurements will continue New drop If checked a new mercury drop is created immediately after applying the first conditioning potential This option is only applicable if an Automatic electrode is selected in the AUTOLAB hardware configuration program Consult the proper Appendix in case a mercury drop electrode is applied Potential or current Potential or current
94. setting is possible Chapter 4 Measurements 55 The impedance is calculated If the applied current range does not match the measured impedance the new best current range is determined and if applicable the measurement is performed again from step 2 10 The results are graphically displayed The pre treatment as well as the measurements can be aborted by clicking the Abort button or by pressing the lt ESC gt key If the FRA settings window is opened it will show whether the measurements are done properly If the greenish button on the tool bar is clicked the monitor plots appear They also give an indication about the quality of the measurement The results of the measurements are plotted in the data presentation window When no plot is loaded the measurements will automatically be presented in a Z versus Z plot See the View option on the data presentation window for other plot types After the measurement the data are now always sorted on frequency Data files measured with older versions of the FRA software version 2 1 are not sorted A sorted data set can be obtained after saving a loaded data file using the option Save work data from the Data presentation window 4 7 Technical background This paragraph explains step by step the measurement sequence which is conducted during the execution of a procedure However more dedicated this time towards the software and hardware internals 1 Load the memory RAM of
95. sion 4 9 The time at which each single frequency is measured can be viewed in ASCII files which can be created See the paragraph on Convert to ASCII 4 5 Single and Multiple Sine waves The applied AC perturbation on top of a DC potential or current can either be a single sine a superposition of five carefully selected sines of different frequencies over one decade or fifteen sines over three decades of frequencies It is advised for common use to choose the single sine wave as perturbation because it gives the best signal to noise ratio The multi sine capabilities can be of use in two particular cases to save time in the low frequency region to record a frequency spectrum at an unstable electrode surface The multiple sine mode can only be used in a limited frequency range The maximum base frequency for the five sine perturbation is 3120 Hz and for fifteen sine perturbation is 312 Hz In both cases the maximum upper frequency is about 31200 Hz 4 6 The measurement sequence The execution of the measurement procedure is conducted through several stages 1 The memory of the DSG is loaded using one of the signal files from disk containing the proper ac signal but is not switched on yet 2 A new drop signal is generated if the hardware configuration shows the presence of a mercury drop electrode see Hardware configuration program 3 The pre treatment starts if one or more conditioning times are unequal to zero and the pr
96. t is incorrect i e an overload occurred or less accurate measurements were recorded the measurement sequence is repeated 9 Depending on whether a repeat of the pre treatment is required the program continues with point 1 or 5 4 10 Measurements at open circuit potential In case the frequency scan is to be measured at open circuit potential OCP the equilibration stage is to be used to apply a potential where the measured current is as low as possible The OCP measured with the cell switched off is applied at the start of the equilibration stage During this stage the potential is continuously adjusted to a value where the current is minimal In case the pre treatment is repeated before each frequency the applied potential may vary from frequency to frequency This feature is enabled with the option Repeat pre treatment before every scan or frequency The algorithm that minimises the current is as follows Ecoarse 1 5 in mV Efine 15 in mV Ncount 15 Number of times Efine is used before return to Ecoarse E Eocr first measured Open circuit potential Estep Ecoarse Read Current PreviousCurrent Current Tel 0 Repeat E E Estep Apply E Read Current if Sign Current lt gt Sign PreviousCurrent then Estep Efine if Estep Efine then Tel Tel 1 if Tel gt Ncount then Tel 0 Estep Ecoarse PreviousCurrent Current Until Equilibration Stage is finished Appendix FRA Data Files The
97. t of the axis labels Double clicking the axis itself allows scaling and positioning of the axis and selection of the axis function Data can be displayed among others as linear inverse og natural log square root inverse square root Except for the linear and og the value 48 User Manual FRA for Windows Version 4 9 of the presented data is modified in real So all subsequent operations are really performed on e g the square root of the data In case of the og not the values but the axis is changed to a logarithmic axis Sometimes it is necessary to perform automatic scaling after changing the axis press FA Double clicking the axis labels allows specification of the format of the axis labels It is very important that the correct precision of the labels is specified When the button I 1 in the upper right corner is clicked the Graph parameter window appears This window allows modification of the relative scale parameters of the so called graph and plotting area and their background colours All changes made to colour and sizes are stored in the default graphics display file Other changes are kept in the procedure file Fig 17 Window which appears after double clicking horizontal axis Horizontal Axis Intercept position Min axis range E Ticks Scale O Major Linear O Ln C Minor O Lg Position O Square root z 1 7 Square root O178X X Square root Y Confirmation LINE ATTRIBUTES
98. te 10 05 1998 Time 16 11 49 5183e 1 1205e 2 90243e 6 86096 Rs ohm Rp ohm CPE F n 7 3 2 0 Chapter 4 Measurements 53 4 Measurements 4 1 Advice on measurements It is advised to switch the potentiostat into High stability mode before the measurements start in case you work with an electrochemical cell with a high capacitive load i e in most cases a high electrode surface area High stability mode offers the potentiostat a better protection for oscillation Oscillations of the potentiostat might destroy your electrode If the applied frequency is too high for high stability the program will automatically switch the potentiostat into High speed mode It is better to start with higher frequencies and then go to lower frequencies It can save time The FRA module will settle at the first applied frequency At very low frequencies this might take quite a long time 4 2 Internal External measurements The FRA2 modules allow doing impedance measurements by passing the built in potentiostat galvanostat The external inputs X and Y can be seen on the front of the module The program supports recording the impedance with respect to an external applied ac signal instead of the applied ac potential For this purpose the applied ac signal should be connected from an external source to the X input Furthermore the checkbox Use external inputs should be clicked on the FRA manual control window Now
99. the digital signal generator DSG The data to fill the memory of the DSG is read from the disk On the disk several files each representing a specific signal type must be present in the signal directory W_SINO1 F01 FRA or W_SGNLO1 F12 and F22 FRA2 a single sine W_SIN02 F01 FRA or W_SGNLO5 F12 and F22 five superimposed sine waves W_SIN03 F01 FRA or W _SGNL15 F12 and F22 FRA2 fifteen superimposed sine waves The datafile contains 16384 FRA or 32728 FRA2 words of 16 bits wide representing the specified signal The content of this file is downloaded in the memory of the DSG The 16 bit DAC is set with a maximum frequency of 3 23 MHz FRA or 32 MHz FRA2 The number of points or DA conversions per sine wave depends on the frequency With the FRA module a single sine is generated with 16384 points when the frequency is below 197 Hz When the frequency is below 976 Hz the FRA2 generates it with 32768 points 56 User Manual FRA for Windows Version 4 9 The amplitude of the signal is controlled by setting the 12 bit multiplying DAC providing a amplitude setting with a resolution of 1 in 4096 The output of the DSG is filtered with a RC filter If the measurements have to be performed by using the autoranging facility the optimal current range is set according to the specified input parameters The selected current range during autoranging depends on the value of the impedance Z The measured value at the s
100. the measured data 1 Load data 2 Choose Fit and Simulation from Analysis menu Data presentation window 3 Make sure that the switch Fit Simulation bottom part of the window is in Fit position 4 Load a previously saved Circuit Description Code Load circuit option from File menu Fit and Simulation window or click the Circuit Description panel to open a sub window to enter the CDC manually 5 Either type in the circuit code or insert one of the standard predefined circuits The predefined circuit is inserted at the cursor position so they can be combined with user defined circuits 6 Press OK in the sub window to return to the Fit and Simulation window The CDC 1s now displayed in the Circuit description panel each element having an ordinal number added to the element s symbol 7 Select elements one by one in the element list below the Circuit description panel Enter the starting value of the parameter or leave the default and choose whether the parameter should be fitted or not If special constraints for element values are necessary change the minimum and maximum allowed values of parameters this may require selecting option Use constraints from Option menu located in Fit and Simulation window 8 Choose whether the fitting should take place in impedance or admittance representation Element parameters are defined independently of the actual representation used 9 Press the Fit button 10 If the fit is not satisfact
101. the plot The removal will be done in all loaded plots With the Resume option on the Plot menu the originally measured data will be reloaded The Save work data option on the File menu can be used to save the selection of the data set Load overlay file This option allows the making of an overlay of one or more previously measured data sets The overlay data will appear in all open graphs The legends of these overlay files are selectable with the overlay legends dropdown box This dropdown box overrules the standard dropdown box where the different potentials currents frequencies are shown A maximum of 3 overlays can be made In case the overlay file contains a potential or current scan a window appears to select a potential current or frequency value depending on the active plot type After clicking the Resume option see above the overlays will disappear Chapter3 The FRA windows 41 Enter text When this option is clicked the Additional text appears in the top left corner of the graph This text can be dragged over the graph After double clicking the field the text itself as well as the format can be modified The first text line of the Paste buffer can be inserted on the text field as well Thus a line of text from the Analysis results window can be copied to the Paste buffer and subsequently inserted there Please note that the text cannot be stored Change axis text A window appears in which the axis description of all pl
102. the top entry point in the help structure For most topics on the screen Help is available By pressing F1 the specific information about the part of the screen on which has been focused is given Tool bar The tool bar contains a list of buttons the current electrochemical method and the name of the current measurement procedure The buttons give short cuts to various menu options which are frequently used Place the mouse pointer on top of a button Its meaning will appear in yellow if pressing the button is allowed The two greenish buttons require some extra explanation They can be pressed during impedance measurements They allow the user to inspect the ac potential and ac current signal in real time domain and in the frequency domain When one or both buttons are pressed monitor plots appear The vertical axis in the time domain plot represents the potential or current as a percentage of the full input range The vertical axis in the frequency domain plot is an arbitrary log scale of the amplitude of the ac signals This plot can be used in order to check whether second harmonic effects occur In case of a single sine signal and low frequency lt 200 Hz the applied sine wave has the index n 1 At higher frequencies the index of the applied signal is equal to the number of sines present within a single cycle When the multiple sine mode is used Chapter 3 The FRA windows 31 the number of applied frequencies is equal to 5 or 15 T
103. ton has been clicked It is advised that during the manual impedance measurements the FRA Settings window is opened as well via the Window menu on the FRA manager window Use external inputs When this box is checked the FRA2 module does not determine the impedance by measuring the current and potential signals from the potentiostat galvanostat Instead the signals applied to the BNC connectors X and Y are measured It is possible that X or Y is connected to the BNC connector Eout or Iout respectively at the rear of the Autolab instrument see also Appendix XI on Hydrodynamic Impedance Measurements 3 6 Data presentation window The Data presentation window serves several functions display of data data analysis data manipulation communication with other programs like Paintbrush Excel or MS Word The window consists of a menu bar a graphical display and a message line As mentioned earlier the measured data are kept in a shared data memory block with the data acquisition software During the measurement the measured data points are also copied to the memory block of the Data presentation window After the measurements the data in this memory block can be modified by options in the Data presentation window However it is always possible to resume the measured data Note that the save options of the File menu of the FRA Manager window always save the measured data The data which can be modified in the Data presentation wi
104. with a factor of 10 compared to High Sens off However in most cases the button position is not relevant High Stability High Speed in High stability mode the PGSTAT is less susceptible to oscillations but its bandwidth is narrower It is advised to switch the potentiostat into High stability mode before the measurements start in case you work with an electrochemical cell with a high capacitive load i e in most cases a high electrode surface area High stability mode offers the potentiostat a better protection for oscillation Oscillations of the potentiostat might destroy your electrode If the applied frequency is too high for high stability the program will automatically switch the potentiostat into High speed mode Potentiostat Galvanostat allows to switch from potentiostatic to galvanostatic It is highly recommended to switch the cell off before switching from one mode to another In case of Potentiostatic control the output of the DAC module corresponds to an applied potential level In case of galvanostatic control an output of the DAC module corresponds to an applied current iR compensation on off Switches iR compensation on or off For impedance measurements iR compensation should be switched off therefore this button cannot be clicked in the FRA program Noise meters The noise levels for current and potential signals are visualised by 2 noise meters at the signal panels When these VU meters are active th
105. y scan is measured at a single dc potential value Potentiostatic potential scan A frequency scan is measured at a set of dc potentials Potentiostatic time scan A frequency scan is made at a fixed potential at regular time intervals Galvanostatic single current A frequency scan is measured at a single dc current value Galvanostatic current scan A frequency scan is measured at a set of dc current values Galvanostatic time scan A frequency scan is made at a fixed current at regular time intervals Chapter 3 The FRA windows 23 Utilities The Utilities menu allows the user to select electrode control burette control RDE control and sleep mode Electrode control The Electrode control option allows the user to operate a static mercury drop electrode which is connected via an IME interface to the Autolab The stirrer can be switched on and off the purge valve can be opened and closed and a mercury drop can be created The Reset button will reset the digital I O port of the Autolab instrument The Purge and Stirrer will be switched off This option is not accessible when no static mercury drop electrode is connected to the Autolab Burette control The burette control option allows the user to control motorburettes connected to Autolab via the DIO48 module Consult the Installation and Diagnostics guide about the type of burettes that can be connected First click the Setup button Then select the burette The displayed Bur

Framan 4.9

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