Chrono methods measurement - Metrohm Autolab The default Chrono amperometry (∆t > 1 ms) and Chrono

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  • Version 1.11.0 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).

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    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 (> 1 ms) Chrono methods

    Chrono methods high speed

    Smallest interval time

    1.3 ms ~ 80 µs/20 µs1 1.33 µs (ADC750) 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

    2 – The Record signals (>1 ms) command

    The Records signals (> 1 ms) command2 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.

    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.

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    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.

    Figure 2 – The complete details of the Record signals (> 1 ms) command

    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).

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    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 time3. 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 2.1.

    2. 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 2.2.

    3. 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 2.3.

    2.1 – 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.

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    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.

    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

    Note

    The same dummy cell will be used for the measurements described in Sections 2.2 and 2.3.

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    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.

    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