Advanced Vanadium Redox Flow Battery Facilitated by Synergistic Effects of the Co₂P-Modified Electrode

Abstract

Redox flow batteries (RFBs) are considered a promising option for large-scale energy storage due to their ability to decouple energy and power, high safety, long durability, and easy scalability. However, the most advanced type of RFB, all-vanadium redox flow batteries (VRFBs), still encounters obstacles such as low performance and high cost that hinder its commercial adoption. One of the factors contributing to the suboptimal performance of VRFBs is the insufficient electrochemical activity of electrodes, which impacts critical metrics including voltage efficiency (VE), energy efficiency (EE), power output, and cycling life. By utilizing cobalt phosphide (Co 2 P) to modify the carbon felt (CF), the resulting Co 2 P-CF composite demonstrates improved electrochemical activity toward the redox reactions of VO 2 + / VO 2+ couple. Theoretical calculations suggest that the adsorption energies of VO 2+ and VO 2 + ions onto Co 2 P-CF are lower than those onto bare CF, facilitating mass transfer in redox reactions. In conjunction with increased specific surface area, enhanced wettability, and improved conductivity, Co 2 P-CF as the cathode enhances the performance of the VRFB compared to that with the use of bare CF electrodes. Specifically, the power density reaches 1011.4 mW cm −2 , representing a 33.5% enhancement over the VRFB cell based on bare CF. During an extended cycling process at 100 mA cm −2 , the Co 2 P-CF-based cell demonstrates average VE and EE values of 88.2% and 86.4%, respectively, surpassing the bare CFbased cell, which exhibits VE and EE values of 76.4% and 74.9%. In this work, the enhancement of the advanced VRFB is achieved by incorporating Co 2 P onto the CF cathode. This approach offers a valuable blueprint for achieving high-performance VRFBs through a straightforward and easily implementable method.