Establishing a pH difference between the two electrolytes (pH decoupling) of an aqueous redox flow battery (ARFB) enables cell voltages exceeding the 1.23 V thermodynamic water-splitting window, but acid–base crossover penalizes efficiency and lifetime. Here we employ mildly acidic and mildly alkaline electrolytes to mitigate crossover, achieving high round-trip energy efficiency with open circuit voltage >1.7 V. We implemented an acid–base regeneration system to periodically restore electrolytes to their initial pH values. The combined system exhibited capacity fade rate <0.07% per day, round-trip energy efficiency >85% and approximately 99% Coulombic efficiency during stable operation for over a week. Cost analysis shows that the tolerance of acid–base crossover could be increased if the pH-decoupling ARFB achieved a higher voltage output and lower resistance. This work demonstrates principles for improving lifespan, rate capability and energy efficiency in high-voltage pH-decoupling ARFBs and pH recovery concepts applicable for pH-decoupling systems.

在水性氧化还原液流电池 (ARFB) 的两种电解质之间建立 pH 值差异（pH 解耦）可以使电池电压超过 1.23 V 热力学水分解窗口，但酸碱交叉会损害效率和寿命。在这里，我们采用弱酸性和弱碱性电解质来减轻交叉，在开路电压 >1.7 V 的情况下实现高往返能量效率。我们实施了酸碱再生系统，以定期将电解质恢复到其初始 pH 值。组合系统在稳定运行一周多的过程中，每天的容量衰减率<0.07%，往返能量效率>85%，库仑效率约为99%。成本分析表明，如果 pH 解耦 ARFB 实现更高的电压输出和更低的电阻，则可以提高酸碱交叉的耐受性。这项工作展示了提高高压 pH 解耦 ARFB 的使用寿命、倍率能力和能源效率的原理以及适用于 pH 解耦系统的 pH 恢复概念。