Hierarchical ZIF-67@NiS grown on nickel foam as a high-performance binder-free electrode for electrochemical capacitors

Abstract

Hierarchical ZIF-67@NiS grown on nickel foam (ZIF-67@NiS-NiF) was successfully synthesized and evaluated as a binder-free electrode for electrochemical capacitor applications. The hybrid architecture integrates the high surface area and redox activity of ZIF-67 with the good electrical conductivity of NiS and the three-dimensional porous framework of Ni foam, facilitating fast charge transfer and efficient ion diffusion. Structural and surface analyses, including XRD, FT-IR, UV-Vis spectroscopy, thermal analysis, SEM, EDXA, and contact angle measurements, confirmed the successful formation, uniform elemental distribution, and enhanced wettability of the composite electrode. Electrochemical studies demonstrated a high specific capacitance of 912 F g⁻¹ at 1 A g⁻¹, good rate capability with 74.6% capacitance retention at 10 A g⁻¹, and excellent cycling stability, retaining 89% of its initial capacitance after 10 000 charge–discharge cycles. Kinetic investigations based on electrochemical impedance spectroscopy showed a low charge-transfer resistance and reduced ion-diffusion resistance, while scan-rate-dependent cyclic voltammetry analysis indicated a dominant capacitive-controlled process with fast redox kinetics. The superior capacitive performance is attributed to the synergistic interaction between ZIF-67 and NiS and the interconnected porous structure of the Ni foam substrate, highlighting the strong potential of ZIF-67@NiS-NiF for high-performance energy storage applications.