ZrO₂‑Nanoparticle-Modified Graphite Felt: Bifunctional Effects on Vanadium Flow Batteries

Abstract

To improve the electrochemical performance of graphite felt (GF) electrodes in vanadium flow batteries (VFBs), we synthesize a series of ZrO₂-modified GF (ZrO₂/GF) electrodes with varying ZrO₂ contents via a facile immersion-precipitation approach. It is found that the uniform immobilization of ZrO₂ nanoparticles on the GF not only significantly promotes the accessibility of vanadium electrolyte, but also provides more active sites for the redox reactions, thereby resulting in better electrochemical activity and reversibility toward the VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox reactions as compared with those of GF. In particular, The ZrO₂/GF composite with 0.3 wt % ZrO₂ displays the best electrochemical performance with voltage and energy efficiencies of 71.9% and 67.4%, respectively, which are much higher than those of 57.3% and 53.8% as obtained from the GF electrode at 200 mA cm^–2. The cycle life tests demonstrate that the ZrO₂/GF electrodes exhibit outstanding stability. The ZrO₂/GF-based VFB battery shows negligible activity decay after 200 cycles