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 ZnMn2O4 (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 m2 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.