Mild pH-decoupling aqueous flow battery with practical pH recovery

摘要

Establishing a pH difference between the two electrolytes (pH decoupling)of an aqueous redox flow battery (ARFB) enables cell voltages exceedingthe 1.23 V thermodynamic water-splitting window, but acid–base crossoverpenalizes efficiency and lifetime. Here we employ mildly acidic and mildlyalkaline electrolytes to mitigate crossover, achieving high round-tripenergy efficiency with open circuit voltage >1.7 V. We implemented anacid–base regeneration system to periodically restore electrolytes totheir initial pH values. The combined system exhibited capacity fade rate85 and approximately 99Coulombic efficiency during stable operation for over a week. Cost analysisshows that the tolerance of acid–base crossover could be increased if thepH-decoupling ARFB achieved a higher voltage output and lower resistance.This work demonstrates principles for improving lifespan, rate capabilityand energy efficiency in high-voltage pH-decoupling ARFBs and pH recoveryconcepts applicable for pH-decoupling systems.