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

Abstract

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.