In Situ Growth of Layered Bimetallic ZnCo Hydroxide Nanosheets for High-Performance All-Solid-State Pseudocapacitor

Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g^-1 at 3 A g^-1 for an electrochemical pseudocapacitor. ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg^-1 at an average power density of 643.8 W kg^-1, which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo_1.5(OH)_4.5Cl_0.5·0.45H₂O nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.