Synthetic Engineering of Manganese Oxide–Carbon Nanocomposites for Maximized Metal Utilization in Supercapacitors

Abstract

Among various electrode materials for supercapacitors, manganese oxide–carbon composites offer a promising balance of cost, performance, and environmental sustainability. Yet while these electrode structures can offer significant overall capacitance, the total capacitance is generally much lower than the theoretically achievable value, highlighting that the manganese oxide is in fact greatly underutilized. This study presents a novel one-pot metal-ammonia synthesis method for fabricating manganese oxide–activated carbon (MnAC) nanocomposites, designed to maximize manganese utilization in supercapacitor electrodes. By leveraging a thermodynamically driven deposition process, Mn3O4 nanoparticles are uniformly anchored onto activated carbon, overcoming limitations of conventional synthesis routes such as poor conductivity and underutilized active materials. The resulting MnAC composites exhibit high specific capacitance (120 F g−1) and 94% capacity retention after 1000 cycles, along with exceptional manganese efficiency (1044 F g−1 relative to Mn content), approaching theoretical limits. Structural and electrochemical analyses confirm the formation of a well-integrated, crystalline Mn3O4 phase with enhanced redox activity and conductivity. This scalable synthesis eliminates toxic solvents and enables ammonia recovery, offering a sustainable pathway for high-performance energy storage materials. The findings highlight the potential of MnAC composites for next-generation supercapacitors and establish a foundation for further optimization of metal oxide–carbon hybrid electrodes.