High-Power Vanadium Redox Flow Battery Based on N-S-Dual Functionalized Graphite Felt

For enhancing the performance of vanadium redox flow batteries (VRFB), nitrogen-sulfur-dual functionalized graphite felt (NSGF) was fabricated using dopamine-based self-polymerization and grafting. The synergistic effect of nitrogen-sulfur dual functionalization was verified via comparison with a graphite felt functionalized with nitrogen only (NGF). The physical characteristics of NSGF were assessed using SEM, TEM, and XPS, and the nitrogen and sulfur were confirmed as existing uniformly on the surface of the electrode. The improved electrochemical activity and reduced polarization of the NSGF was also confirmed, compared with NGF and untreated graphite felt, via CV and EIS. The effect of the surface treatment improved the cell performance of the VRFB. At the current density of 200 mA cm−2, the electrolyte utilization efficiency of the VRFB using NGF showed a 66% improvement, compared to 52% for the untreated graphite felt, whereas the NSGF increased the electrolyte utilization efficiency to 69%. The energy efficiency of VRFB using the NGF was 69%, which was an improvement as compared to 62% for untreated graphite felt; however, NSGF increased the energy efficiency to 72%. The results of this study suggest that surface treatment by nitrogen-sulfur dual functionalization is an effective method for improving the energy efficiency of VRFBs.