Incremental substitution of Ni with Mn in NiFeO to largely enhance its supercapacitance properties.

By using a facile hydrothermal method, we synthesized NiMnFeO nanoparticles as supercapacitor electrode materials and studied how the incremental substitution of Ni with Mn would affect their structural, electronic, and electrochemical properties. X-ray diffractometry confirmed the single-phase spinel structure of the nanoparticles. Raman spectroscopy showed the conversion of the inverse structure of NiFeO to the almost normal structure of MnFeO. Field-emission scanning electron microscopy showed the spherical shape of the obtained nanoparticles with a size in the range of 20-30 nm. Optical bandgaps were found to decrease as the content of Mn increased. Electrochemical characterizations of the samples indicated the excellent performance and the desirable cycling stability of the prepared nanoparticles for supercapacitors. In particular, the specific capacitance of the prepared NiMnFeO nanoparticles was found to increase as the content of Mn increased, reaching the highest specific capacitance of 1,221 F/g for MnFeO nanoparticles at the current density of 0.5 A/g with the corresponding power density of 473.96 W/kg and the energy density of 88.16 Wh/kg. We also demonstrated the real-world application of the prepared MnFeO nanoparticles. We performed also a DFT study to verify the changes in the geometrical and electronic properties that could affect the electrochemical performance.