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.