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

Interfacial H 2 release severely limits the reversibility and feasibility of aqueous Zn metal batteries for large-scale energy storage. Different from the conventional perception that H 2 release mainly originates from the competition between hydrogen evolution reaction and Zn plating process, we herein surprisingly find that non-negligible H 2 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. Based on re-understanding the hydrogen release chemistry of aqueous Zn metal anodes, serious hydrogen release is also generated during Zn stripping process due to accelerated chemical corrosion. To address this issue, after screened organic additives, cysteamine (MEA) was selected as a model additive to in situ construct “chemical barrier” to isolate the interfacial water and consequently enable high Zn/Zn 2+ chemical reversibility. • It is found that non-negligible H 2 is generated during stripping process due to the chemical corrosion of Zn. • Cysteamine additive helps build a gradient solid electrolyte interphase to mitigate the interfacial chemical corrosion. • A positive correlation between adsorption strength and hydrogen release inhibition capability is revealed.