Both ammonium and proton ions may serve as the charge carriers in aqueous ammonium-ion batteries (AAIBs); yet, their respective roles remain elusive. Here, we elucidate the contributions of NH4+ and H+ to the redox behaviors of the copper hexacyanoferrate (CuHCF) electrode using operando pH monitoring, isotopic substitution, and acidity-controlled electrochemical analyses. We identify NH4+ (de)insertion as the bulk redox process, while H+-coupled reactions act as auxiliary interfacial pathways that modulate charge-transfer kinetics. This work highlights interfacial proton management as a key design principle for achieving both high-rate performance and long-term electrochemical stability in aqueous energy-storage systems.
Yang et al. (Thu,) studied this question.