Proton transport mechanism in aqueous hydrogen proton batteries: Unraveling pH-driven thermodynamic/kinetic regulation and acid-free electrolyte design via high-valent cations

This study reveals that electrolyte pH dominates proton concentration and transport kinetics in AHPBs. • At the optimal pH of 2.2, the specific capacity reaches 635.17 mAh g⁻¹, growing by 116.99% against the pH 5.2 baseline. • An Al³⁺-based pH regulation strategy is put forward to substitute strong acids. • It restrains zinc anode corrosion and hydrogen evolution, lifting the cycle life from 220 to 680 cycles (a 209% increase). • The synergistic effect of H⁺ and sulfate ions is clarified, which cuts electrode impedance and narrows charge-discharge voltage gaps, delivering design guidance for high-stable aqueous batteries. Aqueous hydrogen proton batteries (AHPBs) rely exclusively on the electrolyte for proton supply, making electrolyte pH a pivotal parameter governing overall electrochemical performance. In this work, we innovatively establish a continuous electrolyte-pH-gradient experimental system that overcomes the limitations of conventional single-point pH measurements. By integrating systematic electrochemical characterization with mechanistic analysis, we reveal for the first time that the regulation of battery performance by pH stems from the dual direct effect of H + concentration-gradient variations on (i) the thermodynamic equilibrium of the cell electromotive force and (ii) the kinetic process of H + migration. This insight demonstrates that activation of the Grotthuss proton-transport mechanism requires both a proton-rich milieu and a sufficiently dense network of weak hydrogen bonds, thereby deepening the microscopic understanding of H + diffusion pathways. Furthermore, we elucidate the correlation between cation valence state and the dissociation of protons in solvated water, leading to a novel strategy: replacing strong acids with high-valence cations to mitigate the shortened cycle life and low retention observed at low pH. These advances enrich and refine the design philosophy of AHPB electrolytes, opening avenues for acid-free formulations and promising to accelerate the rapid development of AHPB technology.