Facile Hydrothermal Synthesis of NiMn2O4/C Nanosheets for Solid-State Asymmetric Supercapacitor and Electrocatalytic Oxygen Evolution Reaction

Our study presents a facile hydrothermal approach for synthesizing NiMn2O4 and NiMn2O4/C nanostructures (NSs) intended for implementation as electrode materials in high-performance supercapacitors. The NiMn2O4 and NiMn2O4/C NSs synthesized via the hydrothermal method were comprehensively characterized using XRD, FE-SEM, FT-IR, XPS, and BET. Subsequently, the electrochemical performance of both NiMn2O4 and NiMn2O4/C was evaluated via CV, GCD, and EIS in 2 M KOH aqueous electrolyte. Our results demonstrate that the NiMn2O4/C electrode revealed a substantial specific capacitance/capacity of 789.3 F g–1/552.5 C g–1 at a scan rate of 5 mV s–1. Furthermore, the NiMn2O4/C electrode maintained a specific capacity retention of less than 4% after 5000 cycles. When coupled with an activated carbon (AC) electrode, the NiMn2O4/C//AC configuration exhibited a notable specific capacitance/capacity of 101.6 F g–1/162.5 C g–1, accompanied by a high energy density of 36.11 W h kg–1 at a power density of 1000 W kg–1, and sustained excellent cyclic stability (84% retention after 5000 cycles). Additionally, electrochemical analysis revealed an overpotential of 199 mV at 50 mA cm–2 and a minimal Tafel slope of 89 mV dec–1 for the oxygen evolution reaction (OER), suggesting the suitability of the NiMn2O4/C electrode for alkaline water electrocatalysis. Prolonged chronopotentiometry investigations at 100 mA cm–2 over 24 h further demonstrated a remarkable 97.3% retention of the OER activity.