Dynamically Interfacial pH-Buffering Effect Enabled by N-Methylimidazole Molecules as Spontaneous Proton Pumps toward Highly Reversible Zinc-Metal Anodes

Aqueous zinc-metal batteries have attracted extensive attention due to their outstanding merits of high safety and low cost. However, the intrinsic thermodynamic instability of zinc in aqueous electrolyte inevitably results in hydrogen evolution, and the consequent generation of OH- at the interface will dramatically exacerbate the formation of dead zinc and dendrites. Herein, a dynamically interfacial pH-buffering strategy implemented by N-methylimidazole (NMI) additive is proposed to remove the detrimental OH- at zinc/electrolyte interface in real-time, thus eliminating the accumulation of by-products fundamentally. Electrochemical quartz crystal microbalance and molecular dynamics simulation results reveal the existence of an interfacial absorption layer assembled by NMI and protonated NMI (NMIH+), which acts as an ion pump for replenishing the interface with protons constantly. Moreover, an in situ interfacial pH detection method with micro-sized spatial resolution based on the ultra-microelectrode technology is developed to probe the pH evolution in diffusion layer, confirming the stabilized interfacial chemical environment in NMI-containing electrolyte. Accordingly, with the existence of NMI, an excellent cumulative plating capacity of 4.2 Ah cm(-2) and ultrahigh Coulombic efficiency of 99.74% are realized for zinc electrodes. Meanwhile, the NMI/NMIH+ buffer additive can accelerate the dissolution/deposition process of MnO2/Mn2+ on the cathode, leading to enhanced cycling capacity.

Automated summary

A dynamically interfacial pH-buffering strategy using N-methylimidazole (NMI) additive is proposed to eliminate the accumulation of by-products by removing detrimental OH- at the zinc/electrolyte interface. An interfacial absorption layer assembled by NMI and protonated NMI (NMIH+) is found to replenish the interface with protons constantly, resulting in excellent cumulative plating capacity and ultrahigh Coulombic efficiency for zinc electrodes. Additionally, the NMI/NMIH+ buffer additive enhances the dissolution/deposition process on the cathode, leading to enhanced cycling capacity.