Catalytic electrolytes enable fast reaction kinetics and temperature adaptability for aqueous zinc-bromine flow batteries.

Abstract

Catalysts are widely used to improve electrode reactions in static batteries. However, due to aqueous flow batteries utilizing large volumes of electrolytes, previously reported non-flowable solid-phase catalysts are inadequate for addressing challenges such as low conversion ratios and electrolyte failure, especially under low-temperature conditions. Herein, we develop functionalized carbon quantum dot-based colloidal catalytic electrolytes for Zn-Br flow batteries. This approach deviates from conventional catalyst particles anchored on electrodes, which functions both in-electrolyte and at-interface, enhancing interactions between Br-redox pairs and active sites to accelerate Br-based reaction kinetics and optimize low-temperature adaptability. Unlike common Zn-Br systems, those using highly stable carboxyl-functionalized carbon quantum dot catalytic electrolytes exhibit a substantial increase in power density to 389.88 mW·cm^-2. Furthermore, Zn-Br systems incorporating this catalytic electrolyte show a working lifespan of >1982 h (5000 cycles) at 100 mA·cm^-2 and maintain operation at 80 mA·cm^-2 with an energy efficiency of 82.4%. These systems can operate for 1920 h (2000 cycles; energy efficiency: 74.2%) at 40 mA·cm^-2 with minimal capacity decay at -20 °C, attributable to the rearranged hydrogen-bonding networks within catalytic electrolytes. The effectiveness of carbon quantum dot catalytic electrolytes is further validated across various functional groups (carboxyl and hydroxyl).