Effects of in-situ bismuth catalyst electrodeposition on performance of vanadium redox flow batteries

The in-situ electrodeposited bismuth catalyst for vanadium redox flow batteries is typically prepared by dissolving Bi3+ ions in the electrolyte and spontaneously electrodepositing metallic bismuth onto the carbon fiber surface at the beginning of charge process after battery assemble, which therefore has intriguing superiorities including facile preparation, catalyst on-line restoration and long service life. Whether achieving uniform catalyst distribution inside the porous electrode directly influences battery performance. In this work, the effects of the catalyst loading, initial Bi3+ concentration and electrodeposition current density on the catalyst distribution, catalyst morphology and battery performance are comprehensively investigated. It is found that the ratio between the optimal electrodeposition current and theoretical limiting current keeps around 50% for different initial Bi3+ concentrations. The optimal case of constant-current electrodeposition is the initial Bi3+ concentration of 2 mM and electrodeposition current density of 10 mA cm−2. More importantly, the intermittent catalyst electrodeposition method is proposed to address the conflict between electrodeposition current density and catalyst distribution, which delivers superior catalyst distribution and battery performance compared to the optimized constant-current electrodeposition. The battery with intermittent catalyst electrodeposition achieves a high voltage efficiency of 85.4% at 320 mA cm−2.