Controllable synthesis of ultrathin layered transition metal hydroxide/zeolitic imidazolate framework-67 hybrid nanosheets for high-performance supercapacitors

Abstract

Two-dimensional (2D) materials with structures having diverse features are promising for application in energy conversion and storage. A stronger layered orientation can guarantee fast charge transfer along 2D planes and contributes to enhancing the pseudocapacitive properties of the material. Here, we demonstrate a novel one-pot co-precipitation approach to synthesize a hybrid structure comprising a layered transition metal hydroxide (LTMH)/zeolitic imidazolate framework-67 (ZIF-67) (LTMH/ZIF) of ultrathin porous sheet-like nanostructures. The LTMH/ZIF hybrid structures were synthesized with Co²⁺ as the main metal source and Mn²⁺/Ni²⁺/Zn²⁺ as dopants. The ultrathin 2D topography can shorten the path of electron transfer, reduce the diffusion resistance of the electrolyte, and provide more active sites. Among the bimetallic LTMH/ZIF hybrids, α-CoMn_0.05(OH)_x/ZIF-67 displayed a specific capacitance of 689 F g⁻¹ at 0.5 A g⁻¹ in a three-electrode configuration. The as-assembled asymmetric supercapacitor (ASC) (α-CoMn_0.05(OH)_x/ZIF-67//activated carbon (AC)) delivered an outstanding energy density of 79.1 W h kg⁻¹ at a power density of 1350 W kg⁻¹ and reached a high power density of 13 500 W kg⁻¹ with the energy density maintained at 70.5 W h kg⁻¹. The ASC also retained 96.2% of its initial capacity over 3500 cycles. Overall, the proposed strategy enables the preparation of 2D ultrathin LTMH/ZIF hybrid nanostructures, which have great prospects for diverse applications in energy storage.