Proton/hydroxide ion dual-pathway interfacial water regulator-assisted surface stabilization in highly reversible Zn metal batteries

Aqueous Zn metal batteries (AZMBs) are plagued by hydrogen evolution and interfacial alkalization induced by water and its decomposition products (H⁺ and OH⁻), which critically undermine the reversibility and cycling stability of zinc plating and stripping. To address this challenge, oxamic acid (OA), a small bipolar molecule containing both carboxyl and amide groups, is proposed as a multifunctional electrolyte additive. OA forms hydrogen bonds with water molecules, thereby reconstructing the hydrogen-bond network and effectively suppressing both proton transport and hydrogen evolution. Meanwhile, OA dynamically scavenges OH⁻ generated from water decomposition, thus mitigating the generation of alkaline byproducts. Additionally, OA is adsorbed onto the zinc surface, promoting the formation of a water-depleted inner Helmholtz layer and limiting the interfacial reactivity of water. Combined ex situ/in situ characterizations, molecular dynamics simulations, and density functional theory (DFT) calculations collectively verify that OA significantly mitigates parasitic reactions and enhances the stability of the Zn/electrolyte interface. As a result, Zn||Zn cells exhibit over 4000 h of stable cycling at 2 mA cm⁻² and a cumulative plating capacity of 6.875 Ah cm⁻² at 5 mA cm⁻². Zn||Cu cells maintain a high Coulombic efficiency of 99.5% over 4500 cycles, Zn||α-MnO₂ full cells retain 80.1% of their capacity after 2000 cycles, and pouch cells retain 81.5% of their capacity after 600 cycles, highlighting the practical feasibility of this interfacial regulation strategy.