Anomalous hysteresis and current fluctuations in cyclic voltammograms at microelectrodes due to Ag leaching from Ag/AgCl reference electrodes

Abstract

We observe anomalous cyclic voltammograms (CVs) measured with microelectrodes immersed in a Fe(CN)63−/4− redox buffer, which exhibit pronounced hysteresis, current fluctuations, a current level that increases with successive scans, and current suppression at positive potentials in the anodic scan. CV measurements were conducted on electrodes of different sizes under different scan conditions with durations of up to 20 h. By combining these measurements with chemical and surface analysis techniques like Auger Electron Spectroscopy (AES) and Scanning Electron Microscopy (SEM), the observed phenomena were traced to Ag-based leaching from commercial Ag/AgCl reference electrodes. These results indicate that redox interactions at the working electrode can seriously affect CV scans of microelectrodes, and suggest that caution is needed in using Ag/AgCl reference electrodes in electrochemical experiments with small-area working electrodes. Keywords: Reference electrode, Ag/AgCl, Hysteresis, Cyclic voltammetry, Microelectrode, Underpotential deposition