In-situ tailored hierarchical structures of high-mass-loading hydroxide electrode for superior areal performance supercapacitors

Abstract

Designing a high-mass-loading electrode and settling its insufficient stability/low conductivity are urgently needed for the practical application of supercapacitors. Here, MOF-74 with different Z-axis dimensions is assembled by adjusting ligand concentration strategy at the molecular level, followed by an in-situ ion exchange process to fabricate a hierarchically structured Ni(OH)₂/Co(OH)₂ on self-supporting nickel foam (NiCo-NF), reaching an ultra-high mass loading and areal capacitance. The obtained self-supporting NiCo-NF presents a typical 3D hollow structure constituted by 2D ultrathin nanolayers, which can expose the abundant phase interface and a greater number of active sites, leading to an improvement in the utilization efficiency and electrochemical stability of the high-loading electrode. Theoretical calculations and simulations demonstrate that the re-adjustment of charge distribution at the abundant interface effectively promotes charge transfer and enhances electrode reaction kinetics. The high-loading H-NiCo-NF electrode (∼ 23.3 mg cm⁻²) delivers remarkable capacitance (53.6 F cm⁻² at 1 mA cm⁻²), and the M-NiCo-NF electrode (∼ 11.7 mg cm⁻²) shows the considerable capacitance (27.2 F cm⁻² at 1 mA cm⁻²) and structural stability (81.1 % after 7000 cycles). The assembled asymmetric supercapacitor devices show an enhanced OH⁻ storage capability (1.1 mWh cm⁻² and 64.0 mW cm⁻²). Such a functional hierarchical structure of hydroxide shows a new perspective for high areal capacitance self-supported supercapacitors.