In situ mapping of electrochemical activity and oxygen evolution side reaction distribution in aqueous redox flow batteries

Abstract

In aqueous redox flow batteries (ARFBs), the redox reaction of K4[Fe(CN)6]/K3[Fe(CN)6] is commonly applied as an active material for the positive electrode. Its performance is restrained by inhomogeneous electrochemical activity and oxygen evolution side reactions. The activity of both the redox reaction and the side reaction lacks two-dimensional detection method. In this study, ion concentration variations on the electrode surface are converted into refractive index changes by a total internal reflection (TIR) imaging system, which enables characterization of the two-dimensional distributions of surface activity and oxygen evolution reactions (OER) onset potential on the ARFBs positive electrode. This method can obtain the two-dimensional maps of parameters of cyclic voltammetry (CV) and the onset potential of the OER. We validate the feasibility of this method by examining three different electrodes and an electrochemical stability test. This work offers a characterization tool for developing homogeneous electrodes with enhanced activity, high reversibility, and minimized OER side reactions.