Effect of N-S-Functionalization of Graphite Electrode on Electrochemical Performance of Vanadium Redox Flow Battery

The vanadium redox flow battery (VRFB) is under consideration as a promising energy storage system because of its flexible design, long lifetime, and safety against explosion. The electrode in a VRFB plays the essential role of providing reaction sites, which mainly affect the polarization of the system. Insufficient active sites on the surface of the electrode, specifically that made of carbon-based material such as graphite felt and carbon paper, leads to high polarization and poor electrochemical performance. Therefore, several groups have studied methods of electrode surface modification aimed at increasing the number of active sites, such as acid or thermal treatment and introducing of electrocatalyst (noble metal, metal oxide, or carbon-based material) on the electrode surface. In this study, we report a simple and easy method for nitrogen-sulfur dual functionalization on the graphite felt surface to enhance the energy efficiency of VRFB via self-polymerization and graft method. In addition, surface properties were investigated using various analytical techniques, and effect of dual functionalization was examined through comparison with the nitrogen functionalized graphite felt