NiCo-MOF-74 nanoparticle arrays with electrolyte-enhanced interface dynamics for high-rate aqueous energy storage

Abstract

Owing to their large surface area, adjustable framework structures, and multiple redox-active sites, metal-organic frameworks (MOFs) have emerged as attractive candidates for electrodes in aqueous energy storage systems. However, most MOFs suffer from poor electrical conductivity, structural fragility, and limited electrochemical activity, which inhibit their practical application. Herein, we report a novel three-dimensional synergistic regulation strategy to construct high-performance MOF-based electrodes. Specifically, we demonstrate for the first time the in situ growth of NiCo-MOF-74 nanoparticle arrays on flexible carbon cloth via a one-step solvothermal method. Unlike conventional MOF nanowire arrays, the nanoparticle array architecture offers enhanced interfacial contact, shortened ion transport pathways, and superior structural robustness. Density functional theory (DFT) calculations reveal that Co incorporation narrows the bandgap and improves electronic conductivity, supporting the rational design of bimetallic MOF-74 structures. Furthermore, by optimizing the Ni/Co ratio and introducing a redox-active electrolyte additive (K₃[Fe(CN)₆]), the electrochemical kinetics and capacity are greatly enhanced. The optimized electrode delivers a record-high specific capacity of 362.2 mAh g^-1. The corresponding hybrid supercapacitor (HSC) based on NiCo-MOF-74 exhibits a high energy density of 44.7 Wh kg^-1 and outstanding cycling stability (92.5 % after 10,000 cycles). The corresponding alkaline zinc battery (AZB) also shows an excellent energy density of 312.3 Wh kg^-1 with a capacity retention rate of 92 % after 1000 cycles. This work not only introduces a scalable strategy for constructing MOF nanoparticle arrays, but also provides insights into the structure-composition-interface synergy in aqueous energy storage systems.