Study on the performance of MnOx modified graphite felts as electrodes for iron-chromium redox flow battery obtained by permanganic acid etching

Abstract

In order to improve the electrochemical performance of graphite felt electrodes, this paper utilizes the strong oxidizing and corrosive properties of potassium permanganate under acidic conditions to modify graphite felt, and investigates the degree of permanganic-acid's modification of graphite felt at different temperatures as well as the performance of modified graphite felt as an electrode for iron-chromium redox flow batteries. The cyclic voltammetry and electrochemical impedance of the electrodes were tested by a three-electrode system, and the results showed that the introduction of oxygen-containing functional groups reduced the conductivity of the graphite felt, but also the charge transfer impedance. The single-cell test results show that the graphite felt corroded by permanganic-acid at 60 °C has the best performance after assembling the battery, and the discharge capacity and energy efficiency at a current density of 60 mAcm−2 are 41 % and 21 % higher than those of the battery assembled with GF as the electrode. DFT calculations show that the introduction of MnOx can adsorb the active substances in the solution, thus improving the battery efficiency. This method of introducing the number of oxygen-containing functional groups on the surface of graphite felt by temperature modulation and thus obtaining good electrochemical performance of the electrode can provide new ideas for industrial applications.