Regulation of interface reactions at the Zn anode using D-mannosamine hydrochloride as an electrolyte additive

Aqueous zinc-ion capacitors suffer from limited cycling stability because of water-induced side reactions, hydrogen evolution, and dendritic Zn deposition. In this work, D-mannosamine hydrochloride (MAA) was introduced as a multifunctional organic additive into a 2 mol L −1 ZnSO 4 electrolyte. Electrochemical measurements, surface characterization, and density functional theory (DFT) calculations indicate that 0.05 M MAA is the optimized concentration. Rather than significantly reconstructing the bulk Zn 2+ solvation sheath, MAA mainly regulates the Zn/electrolyte interface by preferential adsorption, improved interfacial wettability, reduced direct contact between active water and Zn metal, and more uniform Zn 2+ deposition. The Zn//Zn symmetric cell assembled with the optimized electrolyte cycled stably for 600 h at 1 mA cm −2 and 1 mAh cm −2 . The Zn//Cu asymmetric cell achieved a Coulombic efficiency above 99%. The assembled zinc-ion hybrid capacitor delivered stable cycling for 37,000 cycles at 1 A g −1 . These results demonstrate that low-cost and water-soluble MAA is a promising electrolyte additive for stabilizing Zn anodes in aqueous energy-storage devices.