Application of EIS with Au–Hg microelectrode in determining electron transfer mechanisms

The objective of this study was to investigate the application of microelectrodes with electrochemical impedance spectroscopy (EIS) for distinguishing between one- and two-electron transfer electrochemical reactions occurring within marine microbial biofilms. In our study, both gold and gold–mercury amalgam microelectrodes with tip diameters of 100 μm were used. EIS measurements were performed at the half-wave potentials of the chemicals of interest in 0.5 M NaCl aqueous solutions containing 100 μM each of FeCl3, [Fe(Cat)2]−, [Fe(Cat)3]3−, [Fe(4NCat)3]3−, MnCl2, FeCl2 and mixed solutions with two of those chemicals in NaCl solution or seawater. The results showed that there was a linear relationship between the impedance Zre, Zim and angular frequency ω−1/2 obtained at phase angle of 45° for both one- and two-electron transfer reactions. One-electron transfer reactions could then be distinguished from two-electron transfer reactions by the slopes.