Light-activated binder-free hierarchical NiCoMn oxide on nickel foam for enhanced asymmetric supercapacitor performance

Due to the rapid transition to renewable energy, demand for high-efficiency energy storage systems that simultaneously deliver high power and high energy density is increasing. However, conventional supercapacitors are limited by their inherently low energy density. Overcoming this challenge requires electrode materials with high redox activity, rapid charge-transfer kinetics, and robust cycling stability. In this study, light-activated binder-free hierarchical NiCoMn-Oxide electrodes were directly fabricated on nickel foam via a simple electrodeposition–calcination method, yielding binder-free nanostructured electrodes optimized for efficient supercapacitor applications. Beyond structural optimization, the electrode exhibits a clear photo-assisted electrochemical response, enabling actively tunable charge-storage behavior under UV illumination. The combination of mixed-valence ternary oxide chemistry, binder-free architecture, and photo-induced performance enhancement provides a distinct strategy for advancing next-generation supercapacitor electrodes. XRD analysis confirmed the formation of a crystalline spinel oxide phase, while SEM and TEM images revealed a vertically aligned, porous nanowire network that facilitates ion transport and increases the electroactive surface area. XPS characterization identified multiple oxidation states of Ni, Co, and Mn, indicative of rich pseudocapacitive behavior. The optimized electrode delivered an exceptional specific capacitance of 2724.8 F/g at 5 mV/s and 1327.2 F/g at 3 A g−1. An asymmetric device assembled with activated carbon and the NiCoMn-oxide@NF electrode operated stably up to 2.5 V, achieving an energy density of ~125 Wh/kg at 375 W/kg and retaining ~67% of its capacitance after 5000 cycles. Notably, UV illumination further enhanced charge storage and reduced interfacial resistance, highlighting the material's photo-responsive properties. UV creates electron–hole pairs, increasing carrier density and shifting the quasi-Fermi level (photo-OCP). These carriers reduce Rct (smaller Nyquist semicircle), thereby speeding interfacial redox/charge transfer. These findings demonstrate that well-engineered ternary metal oxide nanostructures can transcend the limitations of conventional supercapacitors, enabling high-performance, durable energy storage devices tailored for next-generation renewable energy integration.