NOVA Technical Note 11 Case study: how to create a 3D potential scan Nyquist plot? 1 3D plotting in NOVA Advanced 3D plotting In NOVA, it is possible to create 2D or 3D plots. To create a 3D plot, three signals must be selected from the available electrochemical signals for the X, Y and Z axis. In a typical impedance measurement performed with NOVA, the following signals are available for plotting (see Figure 1): frequency, Z, -Z, Z, Phase and time. Figure 1 The electrochemical signals available in a typical FRA measurement in NOVA Any of the available signals can be used to create a 3D plot, like a 3D Nyquist plot, for example, using the frequency signal on the Z axis (see Figure 2). Figure 2 A possible 3D plot created in NOVA 1 Page
NOVA Technical note 11 Note The frequency is plotted on the Z axis using a logarithmic scaling. 2 Restrictions There are two important restrictions related to data plotting in NOVA: 1. Only electrochemical signals located in the same data grid can be plotted on a 2D or 3D plot. It is not possible to create a plot using a signal from one experiment for the X axis and a signal from another experiment for the Y axis, even if both experiments are part of the same data set. 2. The signals used on the X, Y and Z axis must have the same length. 3 Adding the DC data to the FRA data grid Taking the two restrictions mentioned in the previous section into account, this technical note will illustrate how to add the DC components in the same data grid as the other impedance data points recorded during a FRA measurement. Using this strategy, each impedance data point will have matching DC potential and DC current values in the data grid. The Autolab FRA potential scan procedure, available in the Autolab group in the procedure editor will be used as a template. The objective of this note is the creation of the 3D potential scan FRA Nyquist plot, similar to the one shown in Figure 3. 2 Page
NOVA Technical Note 11 Figure 3 A 3D potential scan FRA Nyquist plot (experimental data obtained with the Autolab dummy cell) 3.1 Loading the Potential scan FRA procedure Load the Potential scan FRA procedure from the Autolab group of procedures into the procedure editor. Figure 4 shows the overview of the Potential scan FRA procedure. In this procedure, a full frequency scan is performed at twelve different potential values from 1.2 V to 0 V. A step of 100 mv in used in between each measurement. The potential values used in this measurement are defined in the Repeat for each value command. 3 Page
NOVA Technical note 11 Figure 4 Overview of the Potential scan FRA procedure The FRA measurement potentiostatic command is used to perform the frequency scan embedded into the repeat loop. The frequency scan itself is preceded by a Set potential command that defines the DC conditions for the measurement. The Set potential command is linked to the Repeat for each value command (see Figure 4). 3.2 Adding the DC signals to the FRA data In order to add the Potential (DC) and the Current (DC) signals to the FRA data, these signals must first be added to the FRA measurement, for each individual frequency. Open the FRA editor by clicking the button (see Figure 5). 4 Page
NOVA Technical Note 11 Figure 5 Opening the FRA editor In the FRA editor, make sure that the Sample DC property in the Sampler section is set to yes (see Figure 6). 5 Page
NOVA Technical note 11 Figure 6 The DC component is sampled through the FRA editor Note Please refer to the Impedance measurements tutorial, available from the Help menu in NOVA, for a complete description of the signals provided in the FRA sampler. Note The Sample DC option is already set to On in the default Autolab FRA potential scan procedure. Click OK to close the FRA editor window. The procedure editor will be updated and the additional signals will be shown in blue, in the FRA single frequency command (see Figure 8). 6 Page
NOVA Technical Note 11 Figure 7 The additional signals are displayed in blue Note Since the Sample DC checkbox is already checked in the default Autolab FRA potential scan procedure, the Potential (DC) and Current (DC) signals are already available in this procedure (see previous screenshots). When this measurement is performed, the Potential (DC) and the Current (DC) will be logged for each impedance point, thus satisfying the second condition specified at the beginning of this technical note. 3.3 Merging the additional data points to the data grid In order to satisfy the first condition defined at the very beginning of this document, the values of the Potential (DC) and Current (DC) must be added to the data grid containing all the recorded impedance data. 7 Page
NOVA Technical note 11 In order to do this, click the button located next to the Build signal command in the procedure editor, in order to edit the list of signals to extract from the measurement (see Figure 9). Figure 8 Click the button to open the Build signal editor The Build signal editor window will be displayed. The frame on the right hand side shows the list of default impedance values to gather in a single table (see Figure 10). 8 Page
NOVA Technical Note 11 Figure 9 The Build signal window shows the signals to extract from the measurement Expand the Measurement impedance group in the frame on the left hand side and repeat this for the FRA signal frequency group. The Potential (DC) and Current (DC) signals will be shown in the list of signals available (see Figure 11). Figure 10 The additional signals are located in the FRA single frequency group Click the Potential (DC) signal in the frame on the left hand side of the editor and, while holding the mouse button, drag it into the frame on the right hand side. Drop this item just below the FRA single frequency item, as shown in Figure 12. 9 Page
NOVA Technical note 11 Figure 11 Adding the Potential (DC) signal to the list of signals The Potential (DC) will be added to the list of signals collected by the Build signal command (see Figure 13). 10 Page
NOVA Technical Note 11 Figure 12 The Potential (DC) is added to the list of signals Repeat this for the Current (DC), dropping this signal just below the FRA single frequency item in the frame on the right hand side of the Build signal window (see Figure 14). Figure 13 Adding the Current (DC) to the list of signals 11 Page
NOVA Technical note 11 The Current (DC) will be added to the list of signals collected by the Build signal command (see Figure 15). Figure 14 The Current (DC) is added to the list of signals Click OK to validate the changes to the Build signal command. The procedure editor will be updated (see Figure 16). Figure 15 The Potential (DC) and Current (DC) are added to the list of signals located below the FRA measurement potentiostatic command 3.4 Creating the extra plot In order to build an overlay of the 3D Nyquist plots at the end of the measurement, an additional Nyquist plot can be added to the FRA measurement potentiostatic command. 12 Page
NOVA Technical Note 11 From the Plots general group of commands, locate the Custom plot command and add it to the procedure editor, dropping it on the FRA measurement potentiostatic command (see Figure 17). Figure 16 Adding a Custom plot to the FRA measurement potentiostatic command Rename the plot to Nyquist plot 3D, define the X and Y signals to Z and Z, respectively. Link the Z signal to the WE(1).Potential. Change the Show during measurement property from Yes to No (see Figure 18). Figure 17 Defining the plot settings for the Nyquist plot 3D 13 Page
NOVA Technical note 11 Note The plot options of the additional plot can be adjusted as necessary. Note It is not possible to plot the data in 3D in real time. 4 Run the measurement on dummy cell (c) The procedure is now ready. It is possible to save this modified procedure and run it on the Autolab dummy cell (c). This measurement will take roughly 20 minutes. Alternatively, the NOVA technical note 11 - FRA potential scan [NOVA 1.10].nox procedure, provided with this technical note, can be used. More frequencies are included in this procedure. Connect the Autolab dummy cell (c) and press the start button. This experiment takes about 1 ½ hours to complete. When the measurement is complete, an overlay of all the Nyquist 3D plots can be created, resulting in a plot similar to the one shown in Figure 3. 14 Page