Mn-Ni binary metal oxide for high-performance supercapacitor and electro-catalyst for oxygen evolution reaction

Manganese-nickel (Mn-Ni) binary metal oxides are prepared using a hydrothermal technique followed by calcination. X-ray diffraction analysis confirms the formation of two distinct crystalline structures, NiMnO3 and NiMn2O4. The Transmission electron microscope analysis reveals that the as-prepared NiMnO3 exhibits an average size in the range of 50-100 nm. X-ray photoelectron microscope results show that the metal oxides (Mn and Ni) exhibit different oxidation states in the composite. The NiMnO3 exhibits higher electrochemical performance than NiMn2O4 owing to the higher surface area. In a three-electrode configuration, NiMnO3 delivers a capacitance of 230 F g(-1) at 1.0 A g(-1) and withstands 67% of its initial charge storage capability up to 2000 cycles. The asymmetric aqueous two-electrode (NiMnO3/RGO) set-up delivers a capacitance of 33 F g(-1) with an energy density of 8.4 Wh Kg(-1) and power density of 675 W Kg(-1 )at 1 A g(-1). Besides, the NiMnO3 is a good electro-catalyst for oxygen evolution reaction with a low over-potential of 256 mV vs RHE at 10 mA cm(-2) and stable up to 20 h.