Re-understanding and mitigating hydrogen release chemistry toward reversible aqueous zinc metal batteries

Interfacial H₂ release severely limits the reversibility and feasibility of aqueous Zn metal batteries for large-scale energy storage. Different from the conventional perception that H₂ release mainly originates from the competition between hydrogen evolution reaction and Zn plating process, we herein surprisingly find that non-negligible H₂ is also generated during stripping due to the accelerated chemical corrosion of the newly exposed Zn surface. To address this issue, we systematically screened the organic additives with different molecular structures and functional groups. Interestingly, a positive correlation between the adsorption strength of additives and the ability to inhibit the interfacial hydrogen release is found. Taking cysteamine (MEA) as a model additive, a gradient solid electrolyte interphase (SEI) is in situ formed at the Zn surface, acting as a chemical “barrier” to isolate interfacial water molecules from electrode surface consequently enable a higher Coulombic efficiency (> 99.5%, 4000 cycles) compared with that of MEA-free electrolyte (98.1%, 189 cycles). This work provides a new understanding of the interfacial hydrogen release mechanism and the criteria for selecting additives for aqueous Zn metal anodes.