Solid‐State Supercapacitor Device Fabrication Using Optimized Ag‐Doped NiCo 2 O 4 Cathode and Biomass‐Derived Activated Carbon Anode

ABSTRACT In the present work, optimized Ag‐doped NiCo 2 O 4 was used as the cathode and Palmyra‐derived activated carbon as the anode to fabricate a high‐performance solid‐state supercapacitor device. The developed solid‐state configuration demonstrates a significantly enhanced energy density of 78.1 Wh kg −1 and a power density of 793.1 W kg −1 , along with 91% capacitance retention after 10,000 cycles. These values surpass the performance of conventional commercial electric double‐layer capacitors, which typically offer energy densities in the range of 5–10 Wh kg −1 , and exceed many reported gel‐based solid‐state supercapacitor systems. The improved device performance is attributed to the synergistic combination of high‐capacitance pseudocapacitive cathodes, high‐surface‐area porous carbon anodes, efficient electrode‐electrolyte interfacial contact, and optimized charge balance between electrodes. Furthermore, a practical demonstration was carried out by connecting two fabricated devices in series to power an LED, which was continuously illuminated for approximately 90 s, demonstrating the practical energy‐delivery capability of the developed solid‐state supercapacitor. These results highlight the potential of the fabricated device for portable and flexible energy‐storage applications.