Sol-gel engineered diffusion-type nickel cobaltite hollow fibrous electrode for high-capacity hybrid supercapacitors

The development of advanced hybrid supercapacitors (Hy-SCs) demands electrode materials that combine high redox activity with high porosity to achieve both high energy and power densities. In this work, we synthesized hollow microfibrous nickel cobalt oxide (NiCo2O4) via a facile sol-gel approach with the medical fibrous cloth as a disposable template, yielding an interconnected porous network with enhanced surface area and ion-accessible channels. The physicochemical analyses confirmed the formation of a hierarchical hollow microstructure, favoring efficient electrolyte penetration and rapid ion diffusion. The electrochemical properties of microfibrous NiCo2O4 demonstrated a battery-type redox behavior with a maximum specific capacitance of 648.5 F g−1 (383.9 C g−1) at 1 A g−1, with excellent rate capability, retaining 64% capacitance at a high current density of 15 A g−1. When coupled with activated carbon in a two-electrode device, the Hy-SC exhibited a broad voltage window of 1.6 V, delivering an energy density of 21.15 Wh kg−1 and a high-power density of 2750 W kg–1. Moreover, the device sustained 90.9% capacitance retention after 10,000 cycles, highlighting outstanding long-term stability. Utilizing the high energy storage properties, the viability of Hy-SC was validated by powering multiple LEDs for several minutes, underscoring the capability of the device for real-world portable electronics. The scalable and low-cost fabrication route offers a viable pathway for designing hollow, fibrous, redox-type materials for high-performance energy storage systems.