Work function-activated proton intercalation chemistry assists ultra-stable aqueous zinc ion batteries

Abstract

Manganese oxide (MnO_x) cathodes with a Zn²⁺/H⁺ co-intercalation mixing mechanism have exhibited great potential for aqueous zinc-ion batteries (AZIBs) owing to their high energy density and optimal electrolyte suitability. However, the strong electrostatic interactions and slow kinetics between the high charge density zinc ions and the fixed lattice in conventional cathodes have hindered the development of AZIBs. Hence, selecting H⁺ with a smaller ionic radius and reduced electrostatic repulsion as carriers was a feasible strategy. Herein, we developed a series of M-MnO heterojunctions (M = Cu/Co/Ni/Zn) derived from bimetallic metal–organic frameworks (MOF) as cathodes to enable a controllable work function to regulate the proton absorption energy. Therefore, the CO bond derived from the MOF became a fast channel for proton transfer by the bonding effect. Synergistic activation of proton intercalation chemistry by work function and CO bonding. Combined with Density-Functional Theory, the work function exhibited a negative correlation with the proton adsorption energy, which could effectively regulate proton intercalation chemistry. Among them, Cu-MnO delivered optimal electrochemical performance (431.6/150.7 mAh g⁻¹ at 0.2/5.0 A g⁻¹), exhibiting superior cycling stability (98.24 % capacity retention after 12,000 cycles at 5.0 A g⁻¹). This study provided insights into the work function versus proton chemistry for the development of high-performance cathode materials for AZIB.