Cyclic Voltammetry - Setup Parameters

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Cyclic Voltammetry - Setup Parameters

Description

 

8 - PWR Cyclic Voltammetry

 

Parameter

Description

Units

Pstat

Select the potentiostat/galvanostat to perform the experiment. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used.

 

Test Identifier

A string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs. The Identifier string defaults to a name derived from the technique's name. While this makes an acceptable curve label, it does not generate a unique descriptive label for a data set. The Identifier string is limited to 80 characters. It can include almost any normally printable character. Numbers, upper- and lower-case letters, and the most common punctuation characters including spaces are valid.

 

Output File

The name of the file in which the output data are written. By default, it is saved in the default file directory.

 

The input can be a simple file name with no path information. In this case the output file is located in the default file directory. The default file directory is specified in the Gamry.INI file under the [Framework] section with a Key named DataDir. The default path can be changed using the Path command in the Options menu. It can also include path information, such as C:\MY GAMRY DATA\YOURDATA.DTA. In this example, the data are written to the YOURDATA.DTA file in the MY GAMRY DATA directory on drive C. The default value of the Output File parameter is an abbreviation of the technique name with a *.DTA filename extension. We recommend that you use a *.DTA file name extension for your data file names. The data analysis package assumes that all data files have *.DTA extensions.

 

If the script is unable to open the file, an error message box, Unable to Open File, is generated. Common causes for this type of problem include:

•Invalid file name.

•The file is already open under a different Windows® application.

•The disk is full.

 

After you click the OK button in the error box, the script returns to the Setup where you can re-enter the file name.

 

Notes...

Enter several lines of text that describe the experiment. A typical use of Notes is to record the experimental conditions for a data set.

 

Notes defaults to an empty string and is limited to 400 characters. It can include all printable characters including numbers, upper- and lower-case letters, and the most common punctuation including spaces. Tab characters are not allowed in the Notes string. Press the Notes button on the right-hand side to open a separate Notes dialog box.

 

Working Connection

Specify how the potentiostat is connected to the electrochemical cell.

 

Select Positive when the working lead (green) is connected to the positive electrode (discharge cathode) of the electrochemical cell. Select Negative when the working lead (green) is connected to the negative electrode (discharge anode) of the electrochemical cell.

 

Gamry tip bulb

We generally recommend using the Positive option.

 

Initial E

The starting potential of the scan segment. The potential can be specified versus the open-circuit potential (vs. Eoc) or reference electrode potential (vs. Eref).

volts (V)

Scan Limit 1

The first apex potential of the scan segment. Enter the potential either versus the reference electrode potential (vs. Eref) or open-circuit potential (vs. Eoc).

volts (V)

Scan Limit 2

The second apex potential of the scan segment. Enter the potential either versus the reference electrode potential (vs. Eref) or open-circuit potential (vs. Eoc).

volts (V)

Final E

The final potential of the scan segment. The potential can be specified versus the open-circuit potential (vs. Eoc) or reference electrode potential (vs. Eref).

 

The scan segment stops at this value if Scan Limit 2 and Final E are equal.

volts (V)

Scan Rate

The speed of the potential sweep during data acquisition.

 

A practical bound on the Scan Rate is 1000 mV/s. You may try higher scan rates, but they can yield inaccurate data because of the inability of the software to acquire data points fast enough. Scan Rate combined with Step Size determines time between data points, and thus the data acquisition rate in the experiment.

 

 

The maximum data acquisition rate depends on the speed of the computer, the configuration of Windows®, and the other software currently executing. As a guideline, avoid sample times < 100 µs. For scans faster than 1 ms, the acquired data is only displayed after the experiment is dine. This reduces the chance that the computer limits the acquisition speed.

mV/s

Step Size

The spacing between the data points. A typical Step Size setting is between 1 and 5 mV. Use the Step Size parameter and the Scan Range on any given cycle to determine the number of data points:

 

 

The total number of data points must be less than 64 000 for all cycles.

mV

Cycles

The number of times the scan is repeated during the experiment.

 

Conceptually, it is the number of times the potential cycles from the Initial E setting to Scan Limit 1 to Scan Limit 2 to the Final E setting.

 

I/E Range Mode

Select the current range mode and choose between Auto mode or Fixed mode.

 

If set to Auto mode, the I/E Range changes depending on the measured current to optimize the current resolution/error. Auto-ranging does not work well for very small currents or faster sample periods. Do not use Auto mode with sample periods faster than ~1 s.

 

Gamry tip bulb

We recommend Fixed mode, which sets the I/E Range based on the specified Max Current.

 

Max Current

Max Current controls the current measurement range if I/E Range is set to Fixed mode. If I/E Range is set to Auto mode, Max Current specifies the maximum expected starting current.

mA

IR Measure

Determine whether or not to perform IR-measurements during the experiment. When performing an IR-measurement, the current is interrupted and the uncompensated resistance is determined based on the corresponding drop in the voltage measurement. The IR-value is stored in the Vu column of the raw data file.

 

Gamry tip bulb

Do not use this measurement with fast sample periods. As a general rule, any sample period faster than 1 s is too fast for IR-measurements.

 

Init. Delay

The Initial Delay phase of the experiment is the first step to occur in the experimental sequence. This phase of the experiment stabilizes the open-circuit potential of the sample prior to any applied signal and measures that open-circuit potential.

 

The Initial Delay is turned On or Off via the check box in the Setup dialog. The Initial Delay Time parameter is the time that the sample is held at the open-circuit potential prior to the scan. The delay may stop before the Initial Delay Time if the Stability criterion for Eoc is met. The minimum Delay Time time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

 

In many cases, you really do not want to set a delay for a fixed time, but you may want to a delay until Eoc stops drifting. The Stability parameter allows you to set a drift-rate that you feel represents a stable Eoc. If the absolute value of the drift-rate falls below the Stability parameter, the Initial Delay phase of the experiment ends immediately, disregarding the programmed Initial Delay Time. Enter a Stability setting of zero to ensure that the delay will last for the full Initial Delay Time. A typical value is 0.05 mV/s. The upper limit of this parameter is 8 V/s, well above the range of practical stabilities with real cells, while the lower limit is set by your patience. A stability of 0.01 mV/s indicates a drift of less than 1 mV within 100 seconds. The software will always take data long enough to resolve a 1 mV change in the potential at the requested drift rate.

 

No open-circuit voltage measurement occurs if the initial delay is turned off. In this case, the open-circuit voltage defaults to 0.0 V.

seconds (s), mV/s

Conditioning

You may condition the electrode as the first step of the experiment, e.g., to remove an oxide film from the electrode or to grow one. Conditioning ensures that the metal sample has a known surface state at the start of the experiment. This step is done potentiostatically for a set amount of time.

 

Turn the conditioning phase On or Off with the Conditioning switch check box. Conditioning E is the potential applied during the conditioning phase of the experimental sequence. The conditioning potential has an allowed range of ±8 V. The resolution is 0.25 mV. If you have iR-compensation enabled for the data acquisition phase of your experiment, it is also turned on during conditioning. Conditioning E is always specified vs. Eref, because the open-circuit potential is not measured until after Conditioning is completed.

 

The Conditioning Time is the length of time that the sample is potentiostatted at Conditioning E. The minimum time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

seconds (s), volts (V)