Metal-Organic Framework-Derived ZnCoNi-Layered Double-Hydroxide Nanosheets with Charge Storage Characteristics for Supercapacitors

Electrochemical supercapacitors (SCs) are high-efficiencyelectrochemicalenergy storage devices that can deliver energy at a very fast rate.Metal-organic framework (MOF)-derived layered double hydroxides(LDHs) are promising materials with great potential for commercialSC applications. In this study, a two-step synthetic strategy wasdeveloped to produce porous nanostructured ZnCoNi-LDH nanosheets (NSs)from bimetallic MOFs through a chemical reduction method. All theas-synthesized materials were characterized for their crystal structure,phase, morphology, and surface construction. The optimized ZnCo2Ni-LDH composition exhibited the best charge storage abilityand specific capacitance among the different as-synthesized compositions.The specific capacitance of the fabricated device ZnCo2Ni-LDH||cellulose paper-KOH||ZnCo2Ni-LDH was found tobe 348.2 F g(-1) at 1.0 A g(-1), witha maximum energy density of 54.4 W h kg(-1) and apower density of 4439.0 W kg(-1). After 10,000 continuouscharge-discharge cycles, the device retained 86% of its capacitance.It also delivered a high-capacitance-specific Coulombic efficiency(57-60%). A mechanistic study corroborated the experimentalresults that the high pore volume, possible insertion of a greaternumber of electrolyte ions, multioxidation states of Ni and Co ions,and their synergistic effect with Zn2+ all contributedto the diffusion-controlled charge storage behavior. The charge storagecharacteristics of the device were found to be a combination of redoxand electrostatic effects, forming a facile hybrid SC.