In Situ Fabrication of a Uniform Co-MOF Shell Coordinated with CoNiO₂ to Enhance the Energy Storage Capability of NiCo-LDH via Vapor-Phase Growth

Abstract

NiCo-layered double hydroxide (LDH) has attracted increasing attention in recent years for application in supercapacitors (SCs) owing to its high redox activity and intercalating capability. However, the pristine NiCo-LDH is unable to reach theoretical specific capacitance and satisfying rate capability due to the limited electroactive species and a low ion diffusion rate. Here, we demonstrate novel vertically aligned nanosheet arrays of cobalt metal-organic framework (Co-MOF)@CoNiO₂ core-shell composites constructed by the in situ grown Co-MOF shell with a uniform and controlled thickness on the CoNiO₂ core via a vapor-phase approach. Owing to the intimate contact and synergistic effect between the Co-MOF shell and the CoNiO₂ core, the as-synthesized Co-MOF@CoNiO₂ displays a high specific capacitance of about 571 F g^-1, which is significantly higher than the pristine NiCo-LDH electrode (380 F g^-1). Moreover, the capacitive properties of Co-MOF@CoNiO₂ can be further boosted to 757.2 F g^-1 after cyclic voltammetry oxidation. The easy preparation and high electrochemical performance of the Co-MOF@CoNiO₂ composite make it a potential material for SC application. These findings may inspire the exploration and construction of other MOF shell coating metal oxide from various nanostructured LDHs for varied applications. In addition, the as-assembled EO-Co-MOF@CoNiO₂/carbon cloth (CC)//activated carbon (AC) device can achieve a high capacitance of 87.67 F g^-1. Meanwhile, the asymmetric supercapacitor (ASC) device exhibits a high energy density of 27.4 Wh kg^-1 at a power density of 750 W kg^-1.