Raman Cyclic Voltammetry

Introduction

In addition to normal Cyclic Voltammetry tests, the Raman Cyclic Voltammetry experiment allows you to perform CV and spectroscopic measurements simultaneously.

See the Spectroscopy help section for definitions, parameters, and commands for the spectroscopic part. For additional information about setup parameters and commands for corresponding electrochemical experiments, see the Physical Electrochemistry help section.

Setup

The main Raman Cyclic Voltammetry window is:

The Advanced Raman Spectrometer Setup window appears if you activate the Advanced Spec. Setup checkbox:

Parameters for these two windows are:

See the Cyclic Voltammetry experiment for all other parameters.

Experimental Sequence

Run the Raman Cyclic Voltammetry standard technique by selecting the Named Script command under the Experiment menu in Gamry’s Framework™. Opening the Raman Cyclic Voltammetry.exp file initiates the following sequence of events:

1. The Framework creates a runner window, and the Raman Cyclic Voltammetry.exp script is run in this window.
2. The script creates the Setup dialog box and accepts changes in the parameters.
3. The script obtains the use of the spectrometer, and opens the data file specified in theOutput File parameter. The runner window's title reflects the output filename. If the spectrometer is in use or the file cannot be opened, the script returns to the setup dialog box.
4. The file header information is written to the data file. This information is written to the file prior to data acquisition. If the experiment is aborted, the output file contains only this information. This header information includes: a. Tags identifying possible analyses; b. A list of setup parameters
5. The measurement starts if Raw Counts is selected as Spectroscopy Type (skip to number 6). TheNeed to acquire Dark and Blank Spectra window appears if Absorbance or Transmittance is selected as Spectroscopy Type. You can decide if a dark and a blank spectrum should be recorded prior to the actual measurement:



a. If you click the OK button, theAcquire Dark Spectrum window appears.



By clicking OK again, a dark spectrum is recorded. The data of the dark spectrum are not saved. The Acquire Blank Spectrum window appears.



By clicking OK, a blank spectrum is recorded. The data of the blank spectrum are not saved. ARuntime Warning appears.



By clicking OK the actual measurement starts. The previously measured dark and blank spectra are automatically subtracted.

b. If you click the Cancel button, no dark or blank spectra are recorded. For the actual measurement, Raw Counts are measured and plotted versus wavenumber.

6. If Initial Delay is on, the cell is turned off and the specimen's E_oc is measured for the time specified as the Initial Delay time or until the potential stabilizes to a value less than the stability setting. The last measured potential is recorded as E_oc.

A plot of potential versus time is always displayed. A second window for the spectra shows no plot.

If Initial Delay is off, this step is skipped and E_oc is assumed to be 0.0 V vs. Ref.

7. The script conditions the electrode if Conditioning was specified in the setup. Conditioning is done by applying a fixed potential for a defined time while the cell is turned on. A plot of current versus time is displayed during Conditioning. The window for the spectra shows no plot. No data are saved during this step.

8. Finally the data are acquired. The spectrometer starts to measure spectra. Charge and current readings at fixed time-intervals (Sample Period) are taken during the steps in Spectro Chronocoulometry. Plots of charge and current versus time are displayed during the steps. For the spectra, either Raw Counts, Absorbance, or Transmittance are recorded and plotted versus wavelength.

The potential of the sample is set to Initial E and is held at that value for theEquilibration Time. The potential is then swept from the Initial E to Scan Limit 1, then to Scan limit 2, and then to Final E. If Scan Limit 2 equals Final E then the scan stops at that value. If the number of cycles exceeds one, the potential repeats the sweep for n cycles.

Current readings at fixed voltage-intervals are taken during the sweep. The voltage interval between steps is defined as Step Size in the Setup dialog box. The sweep is actually a staircase ramp. The sample is potentiostatically held at Initial E, a delay of one sample period occurs (sample period = 1/Scan Rate × Step Size), and a reading of the current is taken. The potential is then stepped by a few mV as defined by Step Size, a delay of one sample period occurs and the next current reading is taken. Stepping the potential, delaying, and acquiring data points continues until the potential equals Final E.

If you selectedAutoranging in the setup, the current range is automatically switched to the optimal range for the measured cell-current at each point. If Positive Feedback IR-compensation has been selected, all data are continuously corrected for IR-drop. If Current Interrupt IR-compensation has been selected, each potential is corrected for the measured IR-drop of the preceding point.

9. The acquired data are written to the output file and the script cleans up and halts. The script then waits for you to click the F2-Skip button. After you do so, the script closes everything that is open, including the runner window.