Facile Hydrothermal Synthesis of NiMn<sub>2</sub>O<sub>4</sub>/C Nanosheets for Solid-State Asymmetric Supercapacitor and Electrocatalytic Oxygen Evolution Reaction
Pragati N. Thonge, Suprimkumar D. Dhas, Shivaji D. Waghmare, Aravind H. Patil, Teja M. Patil, Manesh A. Yewale, Avinash C. Mendhe, Daewon Kim
Abstract
Our study presents a facile hydrothermal approach for synthesizing NiMn 2 O 4 and NiMn 2 O 4 /C nanostructures (NSs) intended for implementation as electrode materials in high-performance supercapacitors. The NiMn 2 O 4 and NiMn 2 O 4 /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 NiMn 2 O 4 and NiMn 2 O 4 /C was evaluated via CV, GCD, and EIS in 2 M KOH aqueous electrolyte. Our results demonstrate that the NiMn 2 O 4 /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 NiMn 2 O 4 /C electrode maintained a specific capacity retention of less than 4% after 5000 cycles. When coupled with an activated carbon (AC) electrode, the NiMn 2 O 4 /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 NiMn 2 O 4 /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.