Electron-Deficient Sites for Improving V2+/V3+ Redox Kinetics in Vanadium Redox Flow Batteries

Fundamental kinetics of the V2+/V3+ of vanadium redox flow battery (VRFB) are still not well understood despite tremendous efforts in improving the sluggish kinetics of V2+/V3+. This article first reveals the rate-determining step in the electrochemical oxidation of V2+ to V3+ by exploring the reaction kinetics. Thereafter, TiB2 with abundant electron-deficient sites, which possesses a strong electron-accepting ability, is demonstrated to improve the rate-determining step of V2+/V3+ by enhancing the electron transfer from V2+ to the electrode. The mechanism of TiB2 for boosting V2+/V3+ kinetics is also unraveled by analyzing the reaction order. VRFB with the electron-deficient TiB2 demonstrates a remarkable enhancement in the electrochemical performance, exhibiting an excellent rate performance from 70 to 300 mA cm(-2). The energy efficiency is improved by 14.06% compared to the cell with the pristine electrode at 150 mA cm(-2) for 300 cycles. This study is critical for not only proposing the promising electron-deficient catalyst in VRFB application but also promoting fundamental understanding and offering a design strategy for achieving superior performance electrocatalysts in VRFB.