Engineering to disrupt ZIF-67 formation: Novel strategy for constructing hierarchically three-dimensional NiCo-layered double Hydroxide@Co-ZIF-L composites for enhancing energy storage

Abstract

Effective design and construction of highly electrochemically active materials on conductive substrates with hierarchical nanostructures are critical for enhancing the electrochemical energy storage performance of electrodes. However, the design of such special structures is still challenging. In this study, a special three-dimensional@three-dimensional (3D@3D) NiCo-layered double hydroxide (NiCo-LDH) composite nanostructure is developed through the innovative approach of in-situ growth of arrayed Co-Zif-L on conductive substrate, disrupting the Zif-67 formation. This is followed by ion exchange process and electrochemical synthesis for growing 3D NiCo-LDH nanosheets. A unique structure with the 3D NiCo-LDH embedded in the 3D Co-Zif-L structure, termed as 3D@3D, is resulted. This spatial structure not only enhances their mechanical stability and adhesion strength through the in-situ growth process, but also provides a greater number of electrochemical active sites due to its ultra-large specific surface area. Density functional theory (DFT) calculations reveal that the NiCo-LDH@Co-Zif-L composite nanostructure exhibits an enhanced density of states (DOS) near the Fermi level compared to individual components, indicating excellent conductivity. With this unique structure, the NiCo-LDH@Co-Zif-L/NF electrode demonstrates an area-specific capacity of 4.1C cm⁻² and retains 81.9 % of its initial capacitance after 5000 cycles. Moreover, the assembled hybrid supercapacitor achieves an energy density of 222.2 mWh cm⁻² at a power density of 800 mW cm⁻² (66.9 Wh kg⁻¹ at 245 W/kg). The innovative approach in this work provides new insights into the utilization of Zif materials and designing electrode materials with special structures for high-performance electrochemical energy storage devices.