Cyclic voltammetry tutorial
Contents
1. defines the scan rate in Volts per second Signal sampler defines the specific sampler used during the CV staircase By default Time Potential applied and WE 1 Current are measured but additional electrochemical signals can be added to the sampler Moreover the Scan signal which provides the scan number will be added to the data Options defines the options used during the cyclic voltammetry measurement automatic current ranging and cutoffs A Warning Important restrictions in order to properly identify the scans in the data it is important to make sure that the following conditions are respected when defining the parameters of the CV staircase command The Stop potential must be lt than the Upper vertex potential the potential step The Stop potential must be gt than the Lower vertex potential the potential step If these conditions are not respected NOVA will try to adjust the parameters to the closest possible solution but in this case the correct identification of the scan numbers cannot be guaranteed The CV staircase command in NOVA provides a flexible framework for the definition of the scan parameters In a typical cyclic voltammetry experiment it is assumed Because of the maximum sampling rate of the ADC164 module the scan rate in V s divided by the potential step in V should always be lower than 12 000 s with only one signal defined in the sampler 2 Page NOVA Cyclic voltammetry2. removed it is possible to define different values of the start and the stop potential Figure 8 shows an example of a potential profile used during the CV staircase command corresponding to a start potential of O V a stop potential of 0 2 V and a number of stop crossings equal to 3 8 Page NOVA Cyclic voltammetry tutorial Stop crossing 2 Stop crossing 3 Stop crossing 1 WEL Potential V 5 10 15 20 fis 30 35 AQ Time 5 Figure 8 Using different start and stop potentials in the CV sta rcase command The measurement starts at 0 V and stops at 0 2 V The number of stop crossings is three A number of stop crossings equal to 2 would have generated less than half a scan 7 Start potential outside of the scan range A final benefit of the CV staircase command is the possibility of defining a start potential outside of the scan range Figure 9 shows an example of such a potential profile In this example the start potential is 2 V whereas the stop potential is O V Again three stop crossings are required for the first scan to be complete The stop potential value must be unlinked from the start potential Please refer to the User Manual for more information see Section 2 4 4 9 Page NOVA Cyclic voltammetry tutorial 0 5 Stop crossing 1 Stop crossing 3 0 Stop crossing 2 5 omens ar i 1 o 72 10 20 30 At o0 BO Time 5 Figure 9 The CV staircase command allows the start pot
3. Version 1 11 0 NOVA Cyclic voltammetry tutorial 1 Cyclic voltammetry staircase Cyclic voltammetry is the most popular electrochemical method It provides both qualitative and quantitative information as well as a fast and reliable characterization tool The staircase cyclic voltammetry method is a particular format of cyclic voltammetry during which a potential step profile is applied to the electrochemical cell and the response of the cell is measured at the end of each step This allows to measure only the faradaic current since the capacitive current which appears at the beginning of the step arising from the double layer charging has a much higher decay rate 2 The CV staircase command NOVA provides a CY Staircase command which can be used to perform potentiostatic staircase cyclic voltammetry measurements Figure 1 shows an overview of the CV staircase command and its parameters CV staircase 0 000 1 000 1 000 0 000 2 0 1000000 start potential Vv 0 000 Upper vertex potential V 1 000 Lower vertex potential V 1 000 Stop potential V 0 000 Number of stop crossings 2 Step potential V 0 00244 Scan rate V s 0 1000000 Estimated number of points 1650 Interval time s 0 024400 Signal sampler Time WE 1 Current ma Options No Options c Potential applied lt _amay gt V Time lt _amay gt 5 WE 1 Current lt _amay gt A Scan lt _ alray gt Index lt amay gt H i
4. ential can be located outside of the scan range Note The stop potential value must always be located within the scan range defined by the upper and lower vertex potential 8 Circular buffers NOVA uses so called circular buffers in the CV staircase command These buffers have a defined length but can be cycled through an infinite amount of time unlike linear buffers This means that when the number of scans is high the number of data points recorded can exceed the length of the circular buffer This means that only the last X measured data points will be saved at the end of the experiment where X is the length of the circular buffer NOVA will display a warning during validation when the estimated number of points exceeds the length of the circular buffer see Figure 10 10 Page NOVA Cyclic voltammetry tutorial Validation results 0 The following problems were encountered during validation Message Command AUTS0002 4 Number of points exceeds available on board memory Record signals gt 1 ms Number of points exceeds available on board memory Only the last 55555 points will be stored required 100000 OK Cancel Figure 10 A warning is displayed during validation when the circular buffer is exceeded The length of the circular buffer is optimized when the procedure is started in order to maximize the memory use on the embedded processor of the Autolab 11 Page
5. profile applied with the two stop crossings used in the Autolab cyclic voltammetry potentiostatic procedure In the Autolab cyclic voltammetry potentiostatic procedure the stop potential is equal to the start potential 4 Changing the scan direction In the CV staircase command the scan direction is defined by the sign of the step potential If the step potential is positive the scan direction will be from the start potential to the upper vertex potential see Figure 4 If the step potential is negative the scan direction will be from the start potential to the lower vertex potential If the Autolab cyclic voltammetry potentiostatic procedure is repeated using a step potential of 0 00244 V instead of 0 00244 V the potential profile will be identical to the one displayed in Figure 5 5 Page NOVA Cyclic voltammetry tutorial Stop crossing 1 Stop crossing 9 WE 1 Potential tv s 10 15 20 fis 30 39 40 Time s Figure 5 The potential profile applied with the two stop crossings used in the Autolab cyclic voltammetry potentiostatic procedure with a negative potential step It is possible to change the scan direction during a cyclic voltammogram using the Fess button available in the Autolab display see Figure 6 6 Page NOVA Cyclic voltammetry tutorial Autolab display EJ a Autolab manual control AUT40034 Measuring Figure 6 Pressing the S _ button changes the scan direction du
6. ring a measurement The Fess button can be pressed any number of times to reverse the scan direction The measurement stops when the number of stop crossings has been reached 5 Changing the number of scans The number of scans in the CV staircase command is defined by the number of stop crossings This unusual definition of the number of scans has many advantages that will be illustrated in this tutorial Two stop crossings are required for one cycle This means that it is possible to use an odd value as the number of stop crossings in order to perform an extra half scan at the end of the measurement Figure 7 shows the potential profile obtained with the Autolab cyclic voltammetry procedure using three stop crossings instead of two The first two stop crossings define the first cycle and the third stop crossing defines the second half cycle 7 Page NOVA Cyclic voltammetry tutorial stop crossing 2 j Stop crossing 1 Stop crossing 3 WE 1 Potential tv 10 20 30 At ot BO Time Ss Figure 7 The potential profile applied with three stop crossings 6 Using different start and stop potentials Unlike other implementations of the cyclic voltammetry method it is possible with the CV staircase command in NOVA to use a different start and stop potential In the standard Autolab Cyclic voltammetry potentiostatic procedure the start and stop potentials are linked and are therefore identical If the link is
7. se command see Figure 3 Commands Parameters Links Cyclic voltammetry potentiostatic Remarks Cyclic voltammetry potentiostatic End status Autolab Signal sampler Time WE 1 Potential WE 1 Current Options 1 Options Instrument Instrument description Autolab control Set potential Potential V Set cell Wait time s 5 Optimize current range CV staircase Start potential v Upper vertex potential V Lower vertex potential V Stop potential V Number of stop crossings Step potential V 0 00244 Scan rate V s 0 1000000 Estimated number of points 1650 Interval time s 0 024400 Signal sampler Time WE 1 Potential WE 1 Current a Options 1 Options ra Potential applied lt aray gt V Time lt _amay gt 5 WE 1 Current lt _ armay gt A scan lt aray gt WE 1 Potential lt _amay gt v Index lt aray gt ivs E z Set cell Off m ZD Figure 3 The Autolab Cyclic voltammetry potentiostatic procedure The Autolab Cyclic voltammetry procedure performs a single scan from O V to an upper vertex potential of 1 V then to a lower vertex potential of 1 V and finally stopping at a potential of O V The number of stop crossings is 2 Figure 4 shows the potential profile of this experiment 4 Page NOVA Cyclic voltammetry tutorial Stop crossing 2 otop crossing 1 WEL Potential V 5 10 15 20 25 20 35 40 Time 5 Figure 4 The potential
8. tutorial that the start and stop potentials should be the same With NOVA this is not the case anymore and the user is free to define any type a potential scan using the set of parameters available 2 1 Comparison with the Cyclic voltammetry staircase of GPES There are two very significant differences between the Nova Cyclic voltammetry Staircase and the GPES version 1 Nova CV staircase has four different potentials Start Upper vertex Lower vertex and Stop potential The CV in GPES does not have a Stop potential 2 Nova CV staircase does not have a number of cycles but a number of stop Crossings These two differences allow for more flexibility when building a potential profile for cyclic voltammetry The example shown in Figure 2 has the following parameters Start potential 1 2 V upper vertex 1 V lower vertex 0 5 V stop potential 0 8 V number of stop crossings 5 1 4 H Start potential 1 2 W Upper vertex potential 1 M A stop 3 a Stop 1 Stop 2 Stop 4 om Stop 5 Stop potential 0 6 Potential applied W a oD 5 mh Oo N l gt D Lower vertex potential 0 55 W 20 J 20 At 60 50 100 120 Time sS l oo Figure 2 Example of cyclic voltammetry in NOVA 3 Page NOVA Cyclic voltammetry tutorial 3 Using the CV staircase command The standard Autolab Cyclic voltammetry potentiostatic procedure provides a good example of the CV stairca
9. vs E z ie Figure 1 Overview of the CV staircase command Like all the measurement commands the CV staircase command is carefully timed by the Autolab instrument 1 Galvanostatic cyclic voltammetry measurements can be performed using the CV Staircase galvanostatic command 1 Page NOVA Cyclic voltammetry tutorial The CV staircase command has the following parameters Start potential V defines the start potential in Volts The start potential value can be located outside of the scan range defined by the lower and upper vertices Upper vertex potential V defines the upper vertex potential in Volts The upper vertex potential must be higher than the lower vertex potential Lower vertex potential V defines the lower vertex potential in Volts The lower vertex potential must be lower than the upper vertex potential Stop potential defines the stop potential in Volts The stop potential value must be located within the scan range defined by the upper and lower vertices Number of stop crossings defines the number that the scan should cross the stop potential value in order to stop the measurement Step potential V defines the length of the potential step used in the CV staircase command in Volts The step potential can be positive or negative With a positive step the scan starts from the start potential towards the upper vertex potential With a negative step the scan direction is reversed Scan rate V s
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