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The hydrogen evolution reaction and heterogeneous deposition may cause inferior reversibility and stability of the Zn anode for neutral aqueous Zn-metal batteries. Notably, slow reaction kinetics plays a pivotal role in mitigating the Zn2+ concentration gradient and facilitating an elevation in the overpotential for hydrogen evolution. Here, a straightforward electrolyte tactic is implemented to create a predeposition layer characterized by a weak adsorption capability, coupled with an electric double layer featuring a relatively positive charge distribution. This configuration impedes the Volmer reaction and decelerates the deposition reaction kinetics, ultimately mitigating the hydrogen evolution reaction and ensuring a smooth deposition process. Benefiting from the uniform deposition and less hydrogen generation on the Zn anode, replacing 5% Zn2+ with Cd2+ renders a high average Coulombic efficiency in a Zn||Cu battery, a stable cycle in a Zn||Zn battery, and a high-capacity retention in a Zn||MnO2 pouch cell.
Du et al. (Tue,) studied this question.