Energy-Efficient Synthesis of ZnMn ₂ O ₄ Nanoparticles Decorated on Exfoliated Graphite Sheets for High-Performance Asymmetric Supercapacitor

Developing sustainable and efficient electrode materials is vital for advancing clean energy technologies. This study presents a calcination-free, low-temperature coprecipitation method to synthesize ZnMn 2 O 4 (ZMO) nanostructures and their composite with exfoliated graphite (EG) sheets, offering a green and scalable approach for high-performance supercapacitors. EG’s high conductivity, 2D architecture, and mechanical stability significantly enhance the electrochemical performance of ZMO by facilitating faster ion/electron transport, preventing nanoparticle agglomeration, and preserving structural integrity. The optimized composite, ZMOG1, exhibits a high specific capacitance of 680 Fg –1 at 1 Ag –1 and outstanding cycling stability with 96% capacity retention after 10,000 cycles at 7 Ag –1, alongside maintaining 100% Coulombic efficiency. Its large surface area (87.55 m 2 g –1 ) and porous structure further improve ion diffusion. An asymmetric supercapacitor device using ZMOG1 as the cathode, activated carbon as the anode, and PVA-KOH gel as both electrolyte and separator delivers an impressive energy density of 68.5 Wh kg –1 and a power density of 18 kW kg –1 with 96% retention over 60,000 cycles. The ability to power LEDs for several minutes demonstrates the device’s practical application potential, highlighting EG-modified ZMO as a promising next-generation electrode material.