A Universal pH Regulation Principle for HER Suppression in Aqueous Metal Batteries

Hydrogen evolution reactions (HERs) pose a formidable challenge to rechargeable aqueous metal batteries (AMBs), causing flammable gas accumulation and interfacial instability. While conventional buffer-based electrolytes partially mitigate HERs, there lacks a rational pH regulation principle. Herein, we propose a universal pH regulation principle rooted in the equilibrium between soluble metal cations and their hydroxide precipitates, governed by the solubility product (K_sp). Moreover, an analytical platform is designed to quantify the pH-dependent HER kinetics and distinguish the corrosive and catalytic H₂ production by decoupling the evolution of mass, hydrogen gas, and charge. Under this platform, we can identify the optimized pH values (herein, 5.40 in 1 M Zn-based electrolytes) by adding a selective buffer to synchronously suppress both corrosive and catalytic-HERs, leading to evident enhancement of cycling stability. The universality of this principle is also demonstrated in other AMB systems with more serious HER, such as Mn and Mg metal batteries. A more than eightfold increase in cycling lifespan is achieved with tailored buffers in both Mn and Mg AMBs. This work highlights the essential role of pH in aqueous electrolytes and also establishes a thermodynamic foundation for pH optimization and HER mitigation.