1 Chrono methods. The term Chrono methods includes all the measurements of electrochemical signals during a well-defined sequence of steps.

Transcription

1 Version NOVA Chrono methods tutorial 1 Chrono methods The term Chrono methods includes all the measurements of electrochemical signals during a well-defined sequence of steps. In NOVA, time resolved measurements are possible using three different measurement strategies: Using the Record signals (> 1 ms) command: this command can be used at any point in a procedure to record the signals defined in the signal sampler for a specified amount of time and using a well-defined interval time. The smallest possible value of the interval time is 1.3 ms. The Record signals (> 1 ms) command does not apply a potential or current value. It simply samples the signals defined in the sampler using the specified parameters. This tutorial provides more information on the use of the Chrono methods command (see Section 2). Using the Chrono methods command: this command can be used to perform time resolved measurements with interval times smaller than 1.3 ms. The lowest interval time is roughly 80 µs or 20 µs, depending on the type of instrument, and it depends on the type of signals to measure and the number of signals to sample. The measured signals are defined in the signal sampler. This tutorial provides more information on the use of the Chrono methods command (see Section 1). Using the Chrono methods high speed command: this command can be used to perform time resolved measurements at the smallest possible interval time. A dedicated fast sampling ADC module is required for these measurements (ADC750 or ADC10M). The Chrono methods high speed tutorial provided more information on the use of this command in combination with the fast sampling ADC module. The maximum number of signals that can be measured with this methods is two (choice from: WE(1).Potential, WE(1).Current, or External). 1 Page

2 Table 1 provides an overview of some of the important features related to the use of the three different commands for time resolved measurements. Command Record signals Chrono Chrono methods high (> 1 ms) methods speed Smallest interval 1.33 µs (ADC750) 1.3 ms ~ 80 µs/20 µs time 0.1 µs (ADC10M) Setpoint included No Yes Yes Real time display Yes No No Signals selection Sampler Sampler Hardware defined (2) Options support Yes No No Pause/Stop support Yes No No Fast options support Yes No No Time derivative sampling Yes No No Table 1 Comparison of the commands for time resolved commands Scope of the tutorial This tutorial explains how to use the Record signals (> 1 ms) and Chrono methods command in NOVA to perform chrono measurements. Examples for the Autolab dummy cell are provided. 2 The Record signals (>1 ms) command The Records signals (> 1 ms) command 2 is a generic recording command that can be used at any point in a procedure to record the specified signals for a predefined amount of time. Unlike the Chrono methods command, detailed in Section 1, the Records signals (> 1 ms) command does not apply any potential or current value before it starts recording. The Record signals (> 1 ms) command is a timed command. This means that the timing of the measurements will be defined by the internal clock of the Autolab interface. The command can be located anywhere in the procedure editor. The green timing line will be shown on the left of the command to indicate that this is a timed command (see Figure 2). 1 The smallest possible interval time depends on the type of embedded controller used by the instruments. Instruments fitted with the IF030 have a smallest interval time of about 80 µs, while instruments fitted with the IF040 have a smallest interval time of about 20 µs. 2 There are two Records signals (> 1 ms) commands available in the Measurement Chrono methods command group. The Records signals (> 1 ms) command can be used for measurements in potentiostatic mode while the Records signals (> 1 ms) galvanostatic can be used for measurements in galvanostatic mode. In this tutorial, the term Records signals (> 1 ms) will be used for both commands. 2 Page

3 Figure 1 The details of the Record signals (> 1 ms) command The Record signals (> 1 ms) command has the following parameters: Duration: the duration of the measurement, in seconds. Interval time (s): the sampling interval time, in seconds. This value must be smaller than the duration value. The smallest possible value is 1.33 ms. Signal sampler: defines the specific sampler used during the Record signals (> 1 ms) measurement. By default, Time and WE(1).Current are measured, but additional electrochemical signals can be added to the sampler. The Index and Corrected time are automatically added to the data. Use fast options (Yes/No): defines if the fast options are used. By default, this parameter is set to No. Note Additional parameters are available for the Record signals (> 1 ms) command depending on the settings defined in the Signal sampler and the Use fast options parameter (see Figure 2). Figure 2 The complete details of the Record signals (> 1 ms) command 3 Page

4 The following additional parameters are available for Record signals (> 1 ms) command: Fast interval time (s): the fast interval time used to test the options if the Use fast options parameter is set to Yes. If the Use fast options is set to No, then the Fast interval time parameter is not shown (see Figure 1). The value of the Fast interval time must be smaller or equal to the Interval time and it must be an integral fraction of the Interval time 3. The smallest possible value is 1.33 ms (see Section 2.2). dsignal/dt sample threshold (Units/s): specifies the threshold value for the derivative of the specified signal, in units of the signal per second. This parameter is only shown when a time derivative signal is sampled and if the Fast options parameter is set to Yes (see Section 2.3). Depending on the specified parameters, the Record signals (> 1 ms) command can use three different algorithms: 1. Standard parameters (Use fast options set to No): the signals defined in the signal sampler are measured for the specified duration. Each data point is recorded after the user-defined interval time. The measurement options are verified after each interval time. More information is provided in Section Using the fast options (Use fast options set to Yes): the same strategy as in the standard mode is used for measuring the data points but the options are now verified after each user-defined fast interval time. This means that the options can be modified or triggered at a faster rate that the sampling rate. More information is provided in Section Using the fast options and the Time derivative threshold value (User fast options set to Yes and time derivative signals sampled): the same strategy as in the previous mode is used. The time derivative value of one or more signals is determined using the fast interval time. For each time derivative signal, a threshold can be defined by the user. When the absolute value of a time derivative signal exceeds the specified threshold, the data points are measured using the fast interval time instead of the interval time. This means that the sampling rate can be modified depending on the derivative of one or more signals. More information is used in Section Using the Record signals (> 1 ms) command The Record signals (> 1 ms) command is designed to measure the specified signals using the user-defined duration and interval time. To illustrate this, a dummy cell consisting of a resistor of 100 kω in series with a capacitor of 10 µf will be used in this section (see Figure 3). 3 For example, with an interval time of 0.2 s, the fast interval time can be set to 5 ms but not to 7 ms. 4 Page

5 Figure 3 Dummy cell used to illustrate the use of the Record signals (> 1 ms) command This dummy cell has a characteristic RC time of 1 second. The measurements shown in this section are performed using the following procedure: 1. The dummy cell is discharged at 0 V in potentiostatic mode for 10 s. 2. A sequence of 3 current steps is applied on the dummy cell: a. Step 1: 0 µa, for 2 seconds. b. Step 2: 30 µa, for 10 seconds. c. Step 3: -30 µa, for 10 seconds. 3. After each current step, a Record signals (> 1 ms) galvanostatic, as shown in Figure 5 is used. Note The same dummy cell will be used for the measurements described in Sections 2.2 and 2.3. Figure 4 shows the result of a measurement using the standard settings of the Record signals (> 1 ms) command. Figure 4 Measuring the response of the cell 5 Page

6 The RC circuit charges up to 3 V and 3 V during the second and third current step, respectively. The expected potential values are observed after five seconds, which is consistent with the RC time of the cell. Note The default Chrono amperometry ( t > 1 ms) and Chrono potentiometry ( t > 1 ms) procedures provided in the Autolab group of procedures use the Record signal (> 1 ms) command in its standard mode (Use fast options set to No). More information on these procedures is provided in the Getting Started manual. 2.2 Using the fast options and fast interval time The fast options provided by the Record signals (> 1 ms) command can be used to check the options at a faster rate than the sampling rate. When this options is not used (as described in Section 2.1), the options are checked after each sampling interval time. When this option is used, the checking of the options is decoupled from the sampling of the data. This is particularly useful for long measurements on a cell that requires the options to be checked with a short interval time. Figure 5 shows an example of a measurement using a duration of 10 seconds, an interval time of an interval time of 0.2 second. This leads to 50 points. Figure 5 Using the fast options Figure 5 also shows that the fast options are used and that the fast interval time is set to 20 ms. Warning The fast interval time must always be an integral fraction of the interval time. For example, with an interval time of 0.2 s, the fast interval time can be set to 5 ms, but not to 7 ms. 6 Page

7 Using these parameters, a data point will be recorded every 200 ms but the options will be tested every 20 ms. To illustrate this option, the following cutoff conditions will be used (see Figure 6). Figure 6 Cutoff conditions used for the WE(1).Potential signal Note More information on the cutoff options is available in the Cutoff tutorial, available from the Help menu. Two cutoff conditions are used: If the WE(1).Potential is larger (>) than 2.5 V five consecutive times, the command is stopped. If the WE(1).Potential is smaller (<) than -2.5 V five consecutive times, the command is stopped. Figure 7 shows the same measurement as in Figure 4, using the cutoff conditions specified in Figure 6 but without using the fast options. 7 Page

8 Figure 7 Measuring the response of the cell, with the cutoff conditions The Record signals (> 1 ms) commands are interrupted as soon as five consecutive potential values are above 2.5 V or below -2.5 V. Finally, Figure 8 shows the same measurement again, but with the fast options now used. The fast interval time is set to 20 ms in this measurements. Figure 8 Measuring the response of the cell, with the cutoff conditions and the fast options 8 Page

9 The Record signals (> 1 ms) commands are again interrupted by the specified conditions. Comparison with the data shown in Figure 7 reveals that the cutoff condition was triggered as soon as a value higher than 2.5 V or lower than -2.5 V was detected (five consecutive times) by the fast options. Since the fast options uses an interval time of 20 ms, the cutoff is triggered after 100 ms as soon as the measured potential is larger than 2.5 V or smaller than -2.5 V. Figure 8 shows how the cutoff conditions are decoupled from the recording of data points and how the fast options can be used to react on an event in the measurement with a shorter interval time that the interval time used for recording the data. Note When the fast options are used, the number of consecutive detections for a cutoff condition no longer matches actual data points in the measured data. 2.3 Using the time derivative threshold The Record signals (> 1 ms) command offers one additional variation of its sampling algorithm based on the time derivative value of one of more signals. To illustrate this option, the same measurement as described in Section 2.2 will be used in combination with the time derivative of the WE(1).Potential signal. In this example, the interval time is set to 0.2 seconds and the fast interval time is set to 0.02 s. The time derivative of the WE(1).Potential signal is added to the signal sampler (see Figure 9). Figure 9 Adding the time derivative of the WE(1).Potential signal to the list of signals sampled by the Record signals (> 1 ms) command With the Use fast options parameter set to Yes and at least one time derivative signal specified in the sampler, the dx/dt sample threshold parameter is 9 Page

10 automatically added to the Record signals (> 1 ms) command. In the example shown in Figure 10, the dwe(1).potential/dt sample threshold parameter, in V/s, is added to the procedure editor. Figure 10 Using the time derivative threshold Using these parameters, the time derivative of the WE(1).Potential signal will be determined during the measurement using the fast interval time as the dt variation. When the absolute value of the dwe(1).potential/dt, in absolute value is larger or equal to 1 V/s, the data points will be recorded using the fast interval time instead of the interval time. Figure 11 shows the measured data obtained using these parameters. The interval time used in the measurement is 0.2 s for the whole measurement, except at the beginning of the two potential transients, for which an interval time of 20 ms has been used. Figure 11 The results obtained using the time derivate threshold option 10 Page

11 When the WE(1).Potential signal value exceeds 2 V and -2 V, the sampling rate changes. All values measured at the beginning of both transients are measured using the fast interval time. This is highlighted in Figure 12, which shows the data from the first potential transient only (which is shown together with the measured dwe(1).potential/dt signal, plotted on the right-hand side axis). Figure 12 Details of the first potential transient (blue points: E vs t, red line: dwe(1).potential/dt) While the dwe(1).potential/dt value is larger or equal to 1 V/s in absolute value, the recording of the data proceeds with 20 ms interval time instead of the normal 200 ms interval time. 11 Page

12 3 The Chrono methods command Unlike the Record signals (> 1 ms) command, which is used to record electrochemical signals during a single step, the Chrono methods command provides a very flexible framework that can be used to create a sequence of potential or current steps 4. The Chrono methods command is a timed command. This means that the timing of the measurements will be defined by the internal clock of the Autolab interface. The command can be located anywhere in the procedure editor. The green timing line will be shown on the left of the command to indicate that this is a timed command (see Figure 13). Figure 13 The Chrono methods command can be located anywhere in the procedure editor The Chrono methods command is designed to apply a user-defined sequence of steps on the electrochemical cell and record the response of the cell. Depending on the number of data points, transferring the data from the Autolab to the computer can take up to a few seconds. The Chrono methods command is also designed to allow measurement to proceed as quickly as possible, with the highest possible accuracy in interval time. The measured data points can therefore only be shown at the end of the experiment. The Chrono methods command has the following parameters Number of repeats: defines the number of repetitions of the sequence of steps defined in the Levels editor. Signal sampler: defines the specific sampler used during the Chrono methods measurement. By default, Time, Corrected time, Level, Index and WE(1).Current are measured, but additional electrochemical signals can be added to the sampler. 4 There are two chrono methods commands available in the Measurement Chrono methods command group. The Chrono methods command is used for chrono amperometry measurements while the Chrono methods galvanostatic is used for chrono potentiometry measurements mode. In this tutorial, the term Chrono methods will be used for both commands. 12 Page

13 To use the Chrono methods command, the sequence of steps must first be defined. To create or edit a sequence of steps, the button of the Chrono methods command parameter must be clicked (see Figure 14). Figure 14 Opening the Chrono methods editor window The Chrono methods editor window displays two frames (see Figure 15). The frame on the left-hand side contains the sequence of items that will be applied during the measurement. The frame on the right-hand displays the parameters of each element. By default, no items are visible and no parameters are shown (Figure 15). Figure 15 The Chrono methods editor window 13 Page

14 3.1 Creating a sequence of steps The sequence of steps can be constructed by adding items to the sequence, using the five buttons located on the bottom end of the frame on the left-hand side of the window (see Figure 16). Add an item to the sequence Move the highlighted item up in the sequence Remove the highlighted item from the sequence Move the highlighted item down in the sequence Adds a copy of the highlighted item at the end of the sequence Figure 16 The sequence can be edited using the five buttons located in the frame on the left-hand side Five buttons are available in the frame on the left-hand side (see Figure 16): Add ( ): adds an item to the sequence. Remove ( ): removes the highlighted item from the sequence. Copy ( ): creates a copy of the highlighted item at the end of the sequence. Move up ( ): moves the highlighted item up in the sequence. Move down ( ): moves the highlighted item down in the sequence. The following basic items can be used to construct the required sequence (see Figure 16): Step: this item creates a step in the sequence. A step is defined by three parameters the potential (or current), the duration and the interval time. The default values for potential (or current), duration and interval time are 0, s and s, respectively. Level: this item creates a level in the sequence. A level is defined by two parameters the duration and the interval time. The default values are the same as for the step. 14 Page

15 Note The difference between a step and a level is that the level does not have a potential or current parameter. This means that a level does not change the applied potential or current, but only records the electrochemical signals during the indicated duration and with a specific interval time. Note Combining steps and levels is useful for studying the electrochemical response of a system. While a potential step generates a large current spike, the current rapidly decreases and becomes controlled by mass transport. Using a step with a short interval time followed by a level with a long interval time allows you to record the electrochemical signals with an optimal interval time. The Chrono methods editor window also provides two advanced items that can be used to construct elaborated sequences: Repeat (unsampled): this item creates a sub-sequence in the main sequence, in which new items can be added. This sub-sequence can be repeated any number of times, but does not generate any data points, as the electrochemical response of the cell is unsampled for the whole subsequence. This can be useful for conditioning the electrode with a pulse sequence, or for reducing the number of data points recorded during long measurements. Repeat: this item creates a new sub-sequence in the main sequence, in which new items can be added. This sub-sequence can be repeated any number of times and the electrochemical response of the cell is sampled during the whole sub-sequence. To create the required sequence using the Chrono methods editor window, click the button in the frame on the left-hand side and select the required item from the popout menu (see Figure 17). 15 Page

16 A step will be added to the sequence. Figure 17 Adding items to the sequence Click the step that was added to the sequence to display the parameter details in the frame on the right (see Figure 18). 16 Page

17 Figure 18 The details of the step parameters are displayed in the frame on the right Note The parameters of the Step are grouped in two sections: basic and advanced. The step has the following default basic parameters: Text: Step Potential 5 : 0 V Duration (s): Sample: Yes Interval time (s): Estimated number of points: 10 Warning The maximum duration for a single step or level is 4294 seconds. Two additional parameters, Pre Autolab control and Post Autolab control, are advanced settings that can be used to change the Autolab settings during the sequence. These parameters are available in the advanced section and their use falls outside of the scope of this tutorial (see Figure 19). 5 In Galvanostatic mode, the Current parameter is displayed instead of the Potential parameter. 17 Page

18 Figure 19 Advanced parameters are available in the advanced section It is possible to change any of the five parameters of the step. If the duration and/or the interval time are changed, the number of points will be updated accordingly. Change the duration of the step to seconds (see Figure 20). The number of points will be changed to Page

19 Figure 20 Changing the duration or the interval time parameter modifies the number of points Using the same approach, it is possible to add additional steps to the sequence (see Figure 21). Figure 21 Adding more steps to the sequence 19 Page

20 It is also possible to select any item in the sequence and create a copy of it at the end of the sequence by clicking the button in the toolbar. Figure 22 Using the button to copy the highlighted item The copied item is always added at the end of the sequence (see Figure 23). 20 Page

21 Figure 23 The copied item is always added at the end of the sequence The parameters for each step can be edited independently by clicking each individual item in the sequence on the left-hand side. The highlighted item in the sequence is shown in bold lettering (see Figure 24). Figure 24 Editing the parameters of each item in the sequence 21 Page

22 Set the duration of each step to seconds and click the OK button to close the editor and validate the defined sequence. This will update the parameters of the Chrono methods command in the procedure editor view (see Figure 25). Figure 25 The updated parameters of the Chrono methods command in the procedure editor 4 A measurement using the Chrono methods command on the dummy cell A Chrono methods tutorial folder is located in the Program Files\Metrohm- Autolab\Nova 1.11\Shared Databases\Tutorials folder (see Figure 26). Using the database manager, set this folder as the Standard database. Figure 26 Loading the Chrono methods tutorial database 22 Page

23 Seven procedures are included in this tutorial procedure. All the procedures are intended to be used with the standard Autolab dummy cell (see Figure 27). The PGSTAT101 is not equipped with the Autolab dummy cell. An optional external dummy cell can be obtained 6. It is also possible to activate the internal dummy cell, using the Autolab control command 7. Figure 27 The seven Chrono methods tutorial procedures 4.1 CM Tutorial Example 1 Select the CM Tutorial Example 1 procedure from the Standard group. Connect the dummy cell (c) to the instrument and start the measurement. The procedure will perform a measurement on the dummy cell using the following sequence (see Figure 28): Step 1 Potential 0 V, duration s, interval time s. Step 2 Potential 0.3 V, duration s, interval time s. Step 3 Potential -0.3 V, duration s, interval time s. 6 Contact your Autolab distributor for more information. 7 Please refer to the Autolab control tutorial, available from the Help menu, for more information. 23 Page

24 Figure 28 The sequence used in the Example 1 procedure Only the WE(1).Current signal is measured during this experiment. Press the start button to run the measurement. A message box will be displayed before the measurement starts (see Figure 29). Figure 29 The message box shown during the Example 1 tutorial procedure When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 30 shows the expected current profile for this measurement on the dummy cell. 24 Page

25 Figure 30 The current profile plotted vs Corrected time measured during the Example 1 procedure (the data is displayed at the end of the measurement) Note The time scale displayed on the X-axis in Figure 30 has been set to Corrected time. The corrected time is an adjusted time scale for which t = 0 s has been set to first measured data point. The Corrected time signal is available for plotting in the Analysis view. Warning The Chrono methods command automatically calculates a Corrected time signal after the measurement. This signal is a normalized time scale, relative to the absolute time stamp of the first data point recorded during the measurement. This simplifies overlays using data sets from different experiments, since the absolute timing could be different. Close inspection of the measured data in the analysis view reveals that the number of points measured during the Example 1 procedure (147) is smaller than the estimated number of points (150). This discrepancy comes from a small delay generated by the setting of a new potential value at the beginning of each step. This delay is about twice the interval time. 4.2 CM Tutorial Example 2 Select the CM Tutorial Example 2 procedure from the Standard group. Connect the dummy cell (c) to the instrument and start the measurement. The procedure will 25 Page

26 perform the same measurement as the procedure used in the previous example. However, instead of sampling only the WE(1).Current, both the potential and the current are sampled in this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 31 shows the expected current and potential profiles for this measurement on the dummy cell. Figure 31 The current (red curve) and potential (blue curve) profiles plotted vs Corrected time measured during the Example 2 procedure (the data is displayed at the end of the measurement) Careful comparison of the data sets by means of the data grid reveals a significant difference between the two tutorial measurements. Although both measurements have the same duration, seconds, the total number of points is not the same. For Example 1, the total number of points 8 is 147, while the number of points recorded during Example 2 is 66. This difference stems from the settling of the input multiplexer of the ADC164. When more than one signal is sampled, the A/D converter is continuously switching between signals. The switch between signals introduces additional settling and overhead times which increases the achievable interval time. When the practical interval becomes larger than the specified interval time, the data points will be measured as quickly as possible. 8 The total number of points can be slightly different. 26 Page

27 In the case of the data measured during the second tutorial procedure, the number of data points is 66, which corresponds to an interval of roughly 230 µs. Note The timing accuracy of the measurements performed by the Chrono methods commands depends on the number of electrochemical signals sampled during the measurement. Sampling more than one electrochemical signal reduces the number of measurable data points. 5 Using steps and levels There are two types of basic items that can be used in the Chrono methods editor window to build the required sequence of steps for command: steps and levels. This section provides more information on the Level item. A Level is identical to a step except that it does not have a Potential (or Current) parameter. This means that the level will record the electrochemical signals with a given interval time and duration, without changing the applied potential or current. This provides the user with a useful tool to sample the same electrochemical response but with different interval times. Open the Chrono methods editor window, select the last step of the sequence and add a level to the sequence (see Figure 32). 27 Page

28 Figure 32 Adding a level to the sequence Click the level that was added to the sequence to display the parameter details in the frame on the right (see Figure 18). 28 Page

29 Figure 33 The details of the level parameters are displayed in the frame on the right Note The parameters of the Level are grouped in two sections: basic and advanced. The level has the following default basic parameters: Text: Step Duration (s): Sample: Yes Interval time (s): Number of points: 10 Warning The maximum duration for a single step or level is 4294 seconds. The two additional parameters, Pre Autolab control and Post Autolab control, are advanced settings that can be used to change the Autolab settings during the sequence. These parameters are available in the advanced section and their use falls outside of the scope of this tutorial. Change the duration to s and the interval time to s. This will extend the sequence by 10 ms without modifying the applied potential. During this extra time, the electrochemical signals will be sampled using an interval time of 1 ms. 29 Page

30 Click the OK button to close the editor window and update the procedure editor (see Figure 34). Figure 34 The updated procedure editor The procedure editor now indicates that the total duration is s and that the number of points is 160. The extra level that was added to the sequence increases the measurement time by 10 ms, but since it uses a larger interval time, the total number of points is increased by only 10 points. 5.1 CM Tutorial Example 3 Select the CM Tutorial Example 3 procedure from the Standard group. Connect the dummy cell (c) to the instrument and start the measurement. The procedure will perform a measurement similar to the measurement used in the Example 1, but with an extra level at the end of the measurement: Step 1 setpoint 0 V, duration s, interval time s. Step 2 setpoint 0.3 V, duration s, interval time s. Step 3 setpoint -0.3 V, duration s, interval time s. Level no setpoint, duration 0.01 s, interval time s. Only the WE(1).Potential is measured during this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 35 shows the expected potential profile for this measurement on the dummy cell. A combi plot is used to emphasize the change in sampling rate for the level. 30 Page

31 Figure 35 The potential (blue curve) profile plotted vs Corrected time measured during the Example 3 procedure (the data is displayed at the end of the measurement) The potential profile shown in Figure 35 displays the data points collected during the final level in blue. The whole measurement consists of a single data set, but the final part was measured using a larger interval time than the initial part of measurement. The level does not have a setpoint parameter and therefore, there is no potential change between the third step of the sequence and the level. Figure 36 shows a practical example of a chrono amperometry measurement using a level in combination with a step to change the sampling rate. The second step in the experiment is followed by a level with a larger interval time. As the current becomes mass-transport limited, it is not useful to measure the electrochemical response of the cell with a small interval time. Note Using different interval times to record the electrochemical response of the cell is sometimes referred to as decimation or downsampling. 31 Page

32 Figure 36 An example of a measurement using a combination of steps and levels to reduce the number of data points 6 Switching off the sampler An additional feature of the Chrono methods command is that the sampler can be switched off during the sequence. By default, the sampler is on for each basic element in a sequence. However, the user has the choice to switch the sampler on or off for each element in the sequence. This is useful if only a part of the measurement is of interest. Open the Chrono methods window and select the second step. In the parameters frame, change the Sample status from Yes to No (see Figure 37). 32 Page

33 Figure 37 Changing the sample status from Yes to No for the second step Changing the sampling status of the second step sets the estimated number of points to 0. The interval time parameter is also greyed out and cannot be edited anymore. 6.1 CM Tutorial Example 4 The CM Tutorial Example 4 procedure illustrates this option. Select this procedure from the standard group, connect the dummy cell (c) to the instrument and start the measurement. Only the WE(1).Potential is measured during this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 38 shows the potential profile corresponding to this measurement. 33 Page

34 Figure 38 The potential (blue points) profile plotted vs Corrected time measured during the Example 4 procedure (the data is displayed at the end of the measurement) Comparison between Figure 38 and Figure 35 clearly shows that the data from the second step of the sequence is missing. Since nothing is sampled during this step, no potential value is available for plotting. However, the timing of the other elements of the sequence is not affected, since the last step and the following level are correctly located on the time scale. Note Although the second step of the sequence was not sampled in this experiment, the potential of this step was nonetheless applied to the electrochemical cell. The analysis view cannot show this in the plot because sampling was switched off during this step. However, connecting an oscilloscope to the E out connector of the potentiostat clearly shows that the second step is applied during the measurement (see Figure 39). 34 Page

35 V Step 1 Step 2 unsampled Step 3 Level Example 4 Cell off ms -0.5 ms Time Figure 39 Oscilloscope trace measured on the E out connector of the potentiostat showing the applied potential during the measurement of Example 4 (time axis has arbitrary offset) 7 Using Repeat (unsampled) and Repeat There are two types of advanced items that can be used in the Chrono methods editor window to build the required sequence of steps for the Chrono methods command: Repeat (unsampled) and Repeat. Inserting any one of these two items in the sequence editor creates a new subsequence in which new items can be inserted. The main difference between Repeat (unsampled) and Repeat is that the items located in the first sequence are not sampled during the measurement. To add a Repeat (unsampled) item to the sequence, select the last item in the sequence and click the button. Select the Repeat (unsampled) item from the popout menu (see Figure 40). 35 Page

36 Figure 40 Inserting a Repeat (unsampled) item creates a new sequence in the editor A new item will be added to the sequence (see Figure 41). 36 Page

37 Figure 41 The Repeat (unsampled) item creates a new sequence Any item added to the Repeat (unsampled) sequence will be applied but not sampled during the measurement. This provides a framework for introducing a preor a post-conditioning of the electrode during a measurement and for reducing the total number of points during long measurements. Note The Repeat (unsampled) sequence is a useful tool for experiments in which a sequence of steps is repeated many times. Instead of sampling every step, which would generate a lot of data points, the user may prefer to sample only a few steps every now and then (for example two steps every twenty steps). Using the same approach as in the previous examples, select the Repeat (unsampled) item and add two steps using the button (see Figure 42). 37 Page

38 Figure 42 Adding two steps to the Repeat (unsampled) Note The Steps added to the Repeat (unsampled) have the sample status set to No by default. The interval time parameter is greyed out and the estimated number of points is set to 0. It is possible to overrule the sample status, if necessary. Change the potential of the first step of the Repeat (unsampled) sequence to 0.5 and the potential of the second step to Change the duration of both steps to s (see Figure 43). 38 Page

39 Figure 43 Adjusting the parameters of the two steps In this example, the Repeat (unsampled) are intended to be used as a preconditioning stage. Therefore, the whole sequence has to be placed before the three steps and the level of the measurement sequence. Select the Repeat (unsampled) item in the sequence to highlight the whole subsequence (see Figure 44). Note The two Steps located inside the Repeat (unsampled) are also highlighted in dark grey, indicating that these Steps belong to the selected Repeat (unsampled) item. 39 Page

40 Figure 44 Select the Repeat (unsampled) item in the sequence To move this sequence up, click the the left-hand side (see Figure 44). button in the small toolbar in the frame on Figure 45 Click the button to move the selected sub-sequence up in Click the button four times to move it all the w ay at the top of the sequence. 40 Page

41 Select the Repeat (unsampled) and change the number of repetitions to 10. The duration will be updated (see Figure 46). Figure 46 Setting the number of repetitions to 10 for the whole Repeat (unsampled) sequence Click the OK button to close the sequence editor window. The procedure editor will be updated with the new values (see Figure 47). Figure 47 The updated procedure editor 41 Page

42 Note The total number of points does not increase compared to the example shown in Figure 34 because the Repeat (unsampled) does not sample any data points. The number of commands in the sequence is 5: the procedure editor displays the number of items in the main sequence (3 steps, 1 level and 1 Repeat (unsampled)). The total measurement time is updated taking the ten repetitions of the two steps in the Repeat (unsampled) sequence into account. 7.1 CM Tutorial Example 5 The CM Tutorial Example 5 procedure illustrates this option. Select this procedure from the standard group, connect the dummy cell (c) to the instrument and start the measurement. Only the WE(1).Potential is measured during this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 48 shows the potential profile corresponding to this measurement. Figure 48 The potential (blue curve) profile plotted vs Corrected time measured during the Example 5 procedure (the data is displayed at the end of the measurement) The potential profile shown in Figure 48 is identical to the potential profile shown in Figure 35. The reason for this is that nothing is sampled during the Repeat 42 Page

43 (unsampled) sequence and the time is only logged when the sampler is collecting data points. Therefore, the Corrected time scale shown in both plots is the same. Note The total time of the experiment is about 225 ms, while the corrected time scale is only 25 ms. The corrected time scale is based on the first measured data point. Since the steps located in the Repeat (unsampled) sequence are not sampled, the corrected time scale does not include these unsampled steps. The steps located in the Repeat (unsampled) sequence were indeed applied during the measurement. This can be shown by connecting an oscilloscope to the E out connector of the potentiostat (see Figure 49). V Repeat (unsampled) Example 5 Step 1 Step Step 3 Level -1.0 Time ms Figure 49 Oscilloscope trace measured on the E out connector of the potentiostat showing the applied potential during the measurement of example 5. Ten repetitions of the conditioning collection are applied before measurement is started (time axis has arbitrary offset) Click the Figure 50). button to remove the complete Repeat (unsampled) sequence (see 43 Page

44 Figure 50 Click the button to remove the highlighted item from the sequence If a Repeat sequence is used instead of a Repeat (unsampled) sequence, the same behaviour is observed. The Repeat item creates a new sequence to which new items can be added (see Figure 51). 44 Page

45 Figure 51 Inserting a Repeat item creates a new sequence in the editor Items added to the Repeat sequence will be sampled during the measurement. Add two steps to the measurement Repeat sequence and change the potential of the first step to 0.5 V and the potential of the second step to -0.5 V. Change the duration of both steps to s and the interval time to s (see Figure 52). 45 Page

46 Figure 52 Editing the two steps added to the Repeat sub-sequence Note The steps located in the Repeat have the sample status set to on by default. This status can be overruled, if necessary. Set the number of repeats to 1. Click OK to close the chrono methods editor. Click the OK button to close the sequence editor window. The procedure editor will be updated with the new values (see Figure 53). Figure 53 The updated procedure editor 46 Page

47 Note The total number of points increases compared to the previous example (see Figure 47) because the Recurrent steps sequence records data points using the defined sampler. The number of commands in the total sequence is five: three steps, one level and one recurrent steps sequence. 7.2 CM Tutorial Example 6 The CM Tutorial Example 6 procedure illustrates this option. Select this procedure from the standard group, connect the dummy cell (c) to the instrument and start the measurement. Only the WE(1).Potential is measured during this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 54 shows the potential profile corresponding to this measurement. The CM Tutorial Example 6 procedure uses this particular sequence. Select this procedure from the standard group, connect the dummy cell (c) to the Autolab and press the start button. When the measurement is finished, inspect the measured data points in the analysis view. Figure 54 shows the potential profile recorded during this measurement. Figure 54 The potential (blue curve) profile plotted vs Corrected time measured during the Example 6 procedure (the data is displayed at the end of the measurement) 47 Page

48 Since the two final steps are located in a Repeat sequence, they are sampled during the measurement. 7.3 CM Tutorial Example 7 The CM Tutorial Example 7 uses the same sequence as in the Example 5, but instead of using a Repeat (unsampled) sequence, a Repeat sequence is used. Select this procedure from the standard group, connect the dummy cell (c) to the instrument and start the measurement. Only the WE(1).Potential is measured during this experiment. Press the start button to run the measurement. Like in the previous example, a message box is used at the beginning of the measurement. When the measurement is finished, the measured data points will be displayed in the measurement view. Figure 55 shows the potential profile corresponding to this measurement. Figure 55 The potential (blue curve) profile plotted vs Corrected time measured during the Example 7 procedure (the data is displayed at the end of the measurement) The potential profile shown in Figure 55 is the same as the profile recorded on the E out connector of the potentiostat, shown in Figure 49. This illustrates the difference between the unsampled and a normal Repeat sequence in the Chrono methods command. 48 Page