Surface Interface Engineered and Sulfur Source Inspired Carbon Nanofiber Mediated Growth of NSMO Directly on Nickel Foam for Ultra‐High Energy Density Aqueous Asymmetric Supercapacitors

Abstract To advance energy storage technologies, the development of high‐performance supercapacitor electrodes is paramount. This study presents a novel, binder‐free electrode constructed from earth‐abundant materials. A surface interfaced nanocomposite comprising Ni₃S₂ and MnO₂ hierarchical nanostructure (NSMO) is directly grown on carbon nanofibers (CNF) using hydrothermal method. This approach offers scalability and cost‐effectiveness for large‐scale applications. The electrode's exceptional electrochemical performance arises from the synergistic interactions between the mixed oxidation states and composite structure. It exhibits a maximum specific capacitance of 1470 F g⁻¹ at 1 A g⁻¹, coupled with remarkable stability, retaining 78.94% of its capacitance and delivering a Columbic efficiency of 99.5% after 15,000 cycles. When integrated into an asymmetric supercapacitor (ASC), the electrode demonstrated a specific capacitance of 215.7 F g⁻¹ at 1 A g⁻¹, an energy density of 67 Wh kg⁻¹ at a power density of 750 W kg⁻¹, and excellent cycle life. These results highlight the potential of the binder‐free hybrid CNF@NSMO hierarchical nanostructure electrode as a sustainable and high‐performance candidate for next‐generation supercapacitor applications.