Multi-Electrode Configurations for Electrochemical Measurements

Multiple electrodes for standard electrochemical measurements can provide appropriate results depending on the system. Two electrode measurements are common in such systems where the interactions between the anode and the cathode are of interest, such as in batteries.  It is beneficial to understand the capability of three electrode measurements, since this configuration can provide accurate data on a single electrode of interest with respect to a third reference electrode in any system, like in aqueous solution.

The cyclic voltammetry (CV) measurements were performed by the Solartron 1287 at a scan rate of 50 mV/s on a system where a platinum metal counter electrode and a Teflon rod with a circular, planar glassy carbon surface working electrode were immersed in a solution of 0.5 M sodium sulfate (Na₂SO₄). The EIS measurements were performed by the VersaStat 4 potentiostat on an identical system.   

The two electrode CV in Figure 1 show various potentials where anodic and cathodic peaks occur, indicating the presence of oxidation and reduction reactions [1]. The fact that there appears to be two peaks on the voltammogram at about -0.4 V during the forward scan and -0.5 V during the reverse scan suggests that this process is reversible or quasi-reversible [2].

For comparison, a third electrode, a silver/silver chloride (Ag/AgCl) reference electrode, is introduced to the system and a CV is performed, with the results shown in Figure 2.  During the forward scan, the peak at -0.4 V in Figure 1 is hardly visible in the Figure 2 measurement, potentially indicating that there is no significant reaction at the working electrode, although it must be considered that the peak in Figure 1 is a much smaller current density scale. The -0.5 V peak on the reverse scan  remains, albeit resulting in a different current density.  Hence, a possible conclusion can be made in that a change in the rate of reaction at the working electrode is present. 

The EIS measurements in Figure 3 show the comparison of the impedance of two different electrodes using a three electrode system. The impedance measurements were performed using the same electrode setup that was used in the three electrode CV measurements. As expected, the impedance of the carbon electrode was much greater than that of the platinum electrode across the spectrum, especially away from the high frequency end.

Acknowledgment

This work was supported by the FREEDM ERC program of the National Science Foundation under award number EEC-08212121.

References

1. Linden, David, and Thomas B. Reddy. Handbook of Batteries. New York: McGraw-Hill, 2002. Print

2. Jan C. Myland, Keith B. Oldham. Quasi-reversible Cyclic voltammetry of a surface confined redox system: a mathematical treatment. Ont. Canada. 2005