Improved performance of iron-chromium flow batteries using SnO2-coated graphite felt electrodes

Polyacrylonitrile-based graphite felt has the properties of high temperature resistance, corrosion resistance, low thermal conductivity, large surface area and excellent electrical conductivity. It has become the preferred material for flow battery electrodes, but its chemical activity is poor. In order to improve the electrochemical activity of graphite felt electrodes, the electrodes were prepared by SnO2-coated graphite felt. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microscopic morphology of SnO2-coated graphite felt electrodes. Electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge tests were performed using an electrochemical workstation to investigate the electrocatalytic activity of SnO2-coated graphite felt electrodes and their cell performance. The results show that the SnO2 coating on the graphite felt surface forms a convex and concave microstructure, which further increases the specific surface area of the electrode, and at the same time successfully introduces oxygen-containing functional groups to the electrode surface, increasing the electrochemically active spots on the surface. In addition, the presence of oxygen defects in the SnO2 crystal structure provides more electrochemically active sites and improves the electrochemical performance of the graphite felt electrode. At a current density of 142 mA cm−2, the charge-discharge capacity of the battery assembled with the SnO2-coated graphite felt electrode was significantly improved; when the current density was 250 mAcm−2, the Coulombic efficiency of the electrode (TGF-2) coated with a concentration of 0.1 M could reach 84%.