Manipulating cation-water chemistry to inhibit hydrogen evolution of zinc metal anodes

Abstract

The electrochemical behavior of zinc metal anodes is dominated by the interfacial chemistry between the anode and the electrolyte. The local enrichment of cation-solvent complexes with strong interactions in the Helmholtz plane can lead to the evolution of hydrogen on the Zn anode surface during cycling. To tackle this issue, we propose the addition of low doses of N-dimethylformamide (DMF) solvent into 2 M of ZnSO4 electrolyte (D-ZS) to inhibit hydrogen evolution from water splitting and dendrite growth. Molecular dynamics simulation and nuclear magnetic resonance spectroscopy reveal that high donor-number DMF molecules replace part of H2O molecules, thereby reducing the amount of H2O in the solvated sheath of Zn2+. Furthermore, density functional theory calculations demonstrate that DMF increases the lowest unoccupied molecular orbital level of bound water owing to reduced Zn2+ cation-water interaction, preventing the breakage of O−H bond and reducing side reactions of Zn anodes. In addition, the desolvated DMF molecules prefer to adsorb on the zinc anode surface, hindering the migration of Zn2+ to low surface-energy positions that could lead to dendritic formation. As a result, a symmetric cell with D-ZS electrolyte can operate for over 1970 h at 0.5 mA cm−2 for 0.25 mAh cm−2, and Zn-ion hybrid supercapacitors achieve an exemplary cycle performance (93% of capacity retention rate after 30,000 cycles at 2 A g−11). The present work provides a roadmap for regulating electrolyte structure to inhibit hydrogen evolution of zinc metal anodes by manipulating Zn2+ cation-water chemistry.