Characteristics and electrochemical performance of copper/graphite felt composite electrodes for vanadium redox flow battery

Background: Vanadium oxide is considered environmentally benign; however, its economic utilization is highly challenging due to the inability to control the size of etched holes. To address this limitation, it is crucial to regulate the depth of the hole by modifying the etching conditions. A controllable hole depth has the potential to enable its application in vanadium redox flow batteries (VRBs). Methods: In this study, electrodeposition is used to deposit copper particles on the surface of graphite felt electrodes. The copper particles are then employed to etch the graphite felt surface under a reducing atmosphere, which produces porous copper/graphite felt composite electrodes that can be used in VRBs. The effect of etching temperature and time on the material characteristics and the electrochemical performance of this composite electrode were investigated.Significant Findings: The holes on the graphite felt surface following a heat treatment are studied, especially as the temperature approaches 900 degrees C. The observed specific surface area is 16.59 m2/g. Upon grafting of oxygen functional groups, the O/C ratio of the composite electrodes reaches 0.12. After the annealing at 900 degrees C, the energy efficiency of the porous copper/graphite felt composite electrode is 67.40 %, the voltage efficiency is 70.13 %, and the current efficiency is 96.11 %. Under long-term cyclic discharge, the composite electrode exhibits a good capacitance retention of 91 % and a capacitance utilization of 63 %.

Automated summary

Vanadium oxide is an environmentally friendly material, but its economic utilization is challenging due to the inability to control the size of etched holes. In this study, copper/graphite felt composite electrodes with controllable hole depth were prepared by electrodeposition and etching. The composite electrodes exhibited good material characteristics and electrochemical performance under specific etching temperature and time conditions.