High-entropy multimetallic nitrogen-doped carbon for robust ammonium-ion storage

Ammonium ions (NH₄⁺), owing to their abundance, low cost, and environmental friendliness, have emerged as promising non-metallic charge carriers for next-generation aqueous energy storage systems. However, the lack of suitable electrode materials has so far hindered their practical application. In this study, we report the development of a high-entropy multimetallic electrode material comprising uniformly dispersed Mn, Fe, Co, Ni, and Cu species on a conductive graphitized nitrogen-doped carbon framework. This engineered electrode enables high-performance symmetric NH₄⁺-ion supercapacitors. The multi-metal doping strategy significantly increases the density of electroactive sites, reduces NH₄⁺ diffusion barriers, and enhances structural stability. The optimized electrodes deliver a high specific capacitance of 836 F g^-1 at 1 A g^-1 and demonstrate excellent cycling performance, retaining 97.2% of their initial capacity and nearly 100% Coulombic efficiency after 50,000 cycles in a three-electrode system. Moreover, the assembled symmetric devices achieve energy densities exceeding 53 Wh kg^-1 at a power density of 891 W kg^-1. Density functional theory calculations confirm that the synergistic interaction among multiple metal centers optimizes NH₄⁺ adsorption and charge distribution, accounting for the superior electrochemical performance.