Reprint of "Rotating ring-disc electrode measurements for the quantitative electrokinetic investigation of the V3+-reduction at modified carbon electrodes"

Abstract

Thin film rotating-ring disc electrode (RRDE) technique is exploited to quantify the parasitic hydrogen evolution reaction (HER) competing with the desired V3+-reduction at surface modified carbon nanoparticles for application as electrocatalysts in the negative half-cell of vanadium redox-flow batteries (VRFB). Carbon based electrode materials are derived from standard Vulcan XC-72 carbon, treated by chemical surface etching techniques proposed for carbon felt-electrodes in the literature. Additional electrochemical characterization is performed using stationary cyclic voltammetry (CV) followed by fitting of CV data, Fourier-transform alternating-current cyclic voltammetry (FT-ACCV) and electrochemical impedance spectroscopy (EIS) followed by distribution of relaxation times (DRT) analysis. To our knowledge the present paper is the first study using the RRDE technique for separating HER and V3+-reduction reactions. It is demonstrated that the ratio of HER to V3+-reduction significantly depends on the chemical pretreatment of the carbon electrodes and that the V3+-reduction proceeds at an optimum rate at E − ERHE = −0.45 V. Separating the HER from the V3+-reduction also allows us to provide highly accurate values for the diffusion coefficient of the V3+-ion in sulfuric acid solutions.