Highly Conductive Carbon Nanosheets Derived from Rhodanine Pyrolysis-Modified Graphite Felt for Viologen-Based Redox Flow Batteries

Abstract Viologen-based aqueous organic redox flow batteries (AORFBs) are characterized by outstanding electrochemical reactivity. Simultaneously improving the electrical conductivity of electrode materials while maintaining sufficient active surface area is recognized as a viable strategy to enhance the energy conversion efficiency of AORFBs. In this study, graphite felt (GF) was selected as the electrode substrate, and ultrathin carbon nanosheets were synthesized via in situ growth on the surface of graphite felt fibers through in situ pyrolysis of rhodanine, which enables synergistic improvement of the electrical conductivity and electrochemically active area of the resulting electrode. The loading mass of rhodanine was systematically optimized, and the surface chemical composition, microstructure, physicochemical properties, and electrochemical performance of the as-prepared materials were comprehensively characterized. Experimental results demonstrated that the RGF-0.75%-T10 composite electrode exhibits the optimal electrochemical activity toward viologen molecules. A BTMAP-vi/Nme-TEMPO flow cell was assembled to evaluate the practical application potential of the prepared electrodes. In comparison with the battery assembled with pristine graphite felt electrodes, the device constructed with RGF-0.75%-T10 electrodes delivers a substantially reduced charge–discharge overpotential. At a current density of 80 mA cm–2, the voltage efficiency and energy efficiency of the proposed battery reach 80.11% and 79.06% respectively, which are 12.16% and 13.12% higher than those of the pristine graphite felt-based battery. Meanwhile, the peak power density of the assembled battery reaches 113 mW cm–2, which is substantially higher than the 82 mW cm–2 of the battery employing unmodified graphite felt electrodes. This work confirms that constructing electrodes with high electrical conductivity and large active surface area is an effective approach to improve the comprehensive performance of viologen-based aqueous organic redox flow batteries.