Controlled Potential Coulometry - Setup Parameters

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Controlled Potential Coulometry - Setup Parameters

Description

 

4 - Controlled Potential Coulometry

 

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.

 

Electrode Area

The surface area of the sample that is exposed to the solution. The software uses the sample area to calculate the current density and corrosion rate (if applicable). If you do not want to enter an area, we recommend that you leave it at the default value of 1.00 cm².

 

Gamry tip bulb

Do not enter a value of zero!

cm2

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.

 

Pre-step Voltage

The voltage applied in the pre-step before the Step 1 Voltage is applied. Enter the voltage either versus the reference electrode potential (vs. Eref) or open-circuit potential (vs. Eoc).

volts (V)

Pre-step Delay Time

The duration of the pre-step when the Pre-step Voltage is applied.

seconds (s)

Step 1 Voltage

The voltage applied in the first voltage step. Enter the voltage either versus the reference electrode potential (vs. Eref) or open-circuit potential (vs. Eoc).

volts (V)

Step 1 Time

The duration of the first voltage step when Step 1 Voltage is applied.

seconds (s)

Step 2 Voltage

The voltage applied in the second voltage step. Enter the voltage either versus the reference electrode potential (vs. Eref) or open-circuit potential (vs. Eoc).

 

volts (V)

Step 2 Time

The duration of the second voltage step when Step 2 Voltage is applied.

seconds (s)

Sample Period

The spacing between data points. The shortest Sample Period we recommend is 0.1 s. The longest Sample Period allowed is 715 s for Reference potentiostats and 750 s for Interface potentiostats.

 

Use Sample Period to determine the Number of Points in the data curve as follows:

 

 

The Number of Points must be less than 262 143 (218 - 1). If you have more points, the experiment aborts just before the data acquisition phase of the sequence. The resolution in the Total Time is controlled by the Sample Period. Times that are not integer multiples of the Sample Period are rounded down. For example, if the Sample Period is set for 8 seconds, and a Total Time of 900 seconds is requested, the actual Total Time will be 896 seconds, which is 112 Sample Periods.

seconds (s)

Decimate

Enable this option to display the time on a logarithmic scale during the experiment.

 

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

IRComp

Choose to turn iR-compensation either On or Off. Turning on IR Comp causes the applied potential to be adjusted for the estimated iR-drop.

 

Gamry potentiostats are able to estimate uncompensated voltage-drop caused by cell resistance. They do so by performing a current-interrupt experiment after every data point.

 

PF Corr.

The resistance compensated for with positive feedback (PF) selected under IRComp. This value should be between 80–95% of the uncompensated resistance Ru. You cannot compensate for 100% with PF IRComp enabled.

ohm

Expected Max V

The maximum expected voltage which sets the initial voltage measurement range and voltage offset of the galvanostat. If necessary, the voltage measurement range is adjusted during the signal-optimization phase, but this adds extra time to the experiment.

volts (V)

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)

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

Sampling Mode

Select the sampling method for the experiment. Depending on the experiment type, choose between Fast, Noise Reject, and Surface mode.

 

Advanced Pstat Setup

The Advanced Pstat Setup checkbox, if checked, opens the Hardware Settings window, to control specific aspects about your hardware. If you are not an advanced user or simply wish to use the default hardware settings as specified in the scripts, just un-check this box. If you wish to specifically set some hardware items, check this box. The Hardware Settings window opens upon clicking the OK button.

 

Electrode Setup

The Electrode Setup checkbox, if checked, opens the Electrode Setup window, to control specific aspects about your electrode. If you are not an advanced user, or simply wish to use the default electrode settings, just un-check this box. If you need to specifically set the electrode type, the stir/purge conditions, or some hardware items, check this box. The Electrode Setup window opens upon clicking the OK button.