When teaching electrochemistry and electroanalytical chemistry one of the first methods taught in undergraduate courses and labs is cyclic voltammetry.
A classic undergraduate experiment is the recording of a cyclic voltammogram of ferrocyanide. In this note we describe an experiment and results for measuring a cyclic voltammogram on a screen printed carbon electrode (SPCE).
When teaching undergraduate labs the use of SPCE is preferred because:
1) SPCE are a fraction of the cost of glass carbon electrodes etc. - click here.
2) The cost of 1 glassy carbon electrode it is possible to purchase 200 or more SPCE.
3) Electrochemistry is a very practical science with a clear route to commercialisation, therefore the teaching of electroanalytical chemistry using SPCE accelerates students on their route to productization later in their careers.
The practical lab session has two parts:
1) ACTIVATION - Activation of the SPCE to give an activated carbon surface.
2) RECORDING - Recording of the voltammetry.
To obtain the best possible results from the SPCE, first activate the surface.
Activation
The activation process is to polarise/apply a potential of 1.25 V to the working electrode versus the onboard reference electrode for 300 seconds. The activation solution was 1 M NaOH. After activation the electrode was rinsed with deionized water, and then it was ready to use.
Experiment
In Figure 1 a series of voltammograms are shown, these voltammograms are recorded on an activated hyper value screen printed carbon electrode electrode from ZP. The electrode were activated for 300 seconds before initiating the series of voltammetric experiments. The activation of the carbon surface is achieved using the conditions described above.
Analysis of the voltammograms
For a simple reversible redox process the peak height of the anodic and cathodic peaks are expected to be proportional to the square root of the scan rate. If we consider Figure 2 we can see that the anodic peak height and the cathodic peak heights are proportional to the square root of the scan rate. The relationship between redox peak heights is line with Randles- Sevcik equation, and this indicates that the peak heights are under diffusion control. Further the peak height of the anodic and cathodic are the same as can be seen the peak height ratio analysis in Table 1.
In a truly reversible electrochemical redox reaction then the anodic peak to cathodic peak separation is approximately 59.2 mV/no. of electrons. If we consider Table 1 we see that the peak separation is approximately 75 mV, which suggests that the process is not reversible but rather is quasi-reversible. The data suggests that a reversible process maybe obtained by reducing the scan rate to approximately 1 mV/s.
Table 1
Figure 1
Figure 2