Metal–Organic\nFramework-Derived ZnCoNi-Layered\nDouble-Hydroxide Nanosheets with Charge Storage Characteristics for\nSupercapacitors

Abstract

Electrochemical supercapacitors (SCs) are high-efficiency\nelectrochemical\nenergy storage devices that can deliver energy at a very fast rate.\nMetal–organic framework (MOF)-derived layered double hydroxides\n(LDHs) are promising materials with great potential for commercial\nSC applications. In this study, a two-step synthetic strategy was\ndeveloped to produce porous nanostructured ZnCoNi-LDH nanosheets (NSs)\nfrom bimetallic MOFs through a chemical reduction method. All the\nas-synthesized materials were characterized for their crystal structure,\nphase, morphology, and surface construction. The optimized ZnCo₂Ni-LDH composition exhibited the best charge storage ability\nand specific capacitance among the different as-synthesized compositions.\nThe specific capacitance of the fabricated device ZnCo₂Ni-LDH||cellulose paper-KOH||ZnCo₂Ni-LDH was found to\nbe 348.2 F g^–1 at 1.0 A g^–1, with\na maximum energy density of 54.4 W h kg^–1 and a\npower density of 4439.0 W kg^–1. After 10,000 continuous\ncharge–discharge cycles, the device retained 86% of its capacitance.\nIt also delivered a high-capacitance-specific Coulombic efficiency\n(57–60%). A mechanistic study corroborated the experimental\nresults that the high pore volume, possible insertion of a greater\nnumber of electrolyte ions, multioxidation states of Ni and Co ions,\nand their synergistic effect with Zn²⁺ all contributed\nto the diffusion-controlled charge storage behavior. The charge storage\ncharacteristics of the device were found to be a combination of redox\nand electrostatic effects, forming a facile hybrid SC.