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Doping in transition metal oxides open an opportunity to tailor their properties for energy storage application. In this work, Fe doped NiCo2O4@rGO (Fe-NiCo2O4@rGO) nanosheets network were prepared and investigated as electrode for supercapacitor. It is found that Fe doping generates rich oxygen vacancies while addition of rGO increases the surface area. Moreover, DFT calculations show the improved conductivity as well as increase in active sites leading to improved reaction kinetics. These features make Fe-NiCo2O4@rGO nanosheets an exceptional candidate as an electrode material for supercapacitors. It has been revealed that Fe-NiCo2O4@rGO electrode delivered higher specific capacitance of 1252 F g−1at a current density of 1 A g−1in 1.0 M neutral Na2SO4solution, as compared to Fe-NiCo2O4(950 F g−1) and NiCo2O4(610 F g−1) electrodes. Interestingly, the assembled asymmetric coin cell supercapacitor (Fe-NiCo2O4@rGO//AC) delivers superb specific capacitance of 182 F g−1at 1 A g−1and achieved an outstanding energy density of 57.1 Wh kg−1at a power density of 670.5 W kg−1. Moreover, the device retains its stability for 10,000 cycles at 4 A g−1with a capacitance retention of 94.3 %. These results suggest that Fe-NiCo2O4@rGO nanosheets network could be an emerging electrode material with high feasibility value for future energy storage systems, especially supercapacitors.

In this work, Zn-doped δ-MnO2(ZnMO) flower-like nanostructures on carbon fibers are synthesized by one-pot hydrothermal method. It is found that insertion of Zn ions induces oxygen vacancy defects, increase in active sites and conductivity of δ-MnO2(MO) structure. These features making ZnMO structure an excellent candidate for the fabrication of electrode material for supercapacitors. It has been revealed that ZnMO@CC electrode delivered an enhanced specific capacitance of 667 F g−1at a current density of 1 A g−1as compared to the pristine δ-MnO2and previously reported nanostructures. The developed asymmetric coin cell supercapacitor (ZnMO//AC) obtained a specific capacitance of 116 F g−1at 1 A g−1and achieved an outstanding energy density of 71.5 Wh kg−1at a power density of 1067.1 W kg−1. Moreover, the device retains its initial capacitance of 92 % after 8000 cycles at 8 A g−1. These results suggest that ZnMO could be an emerging electrode material for the fabrication of high-performance supercapacitors for practical applications. This research hunts for new visions for the preparation of MnO2-based material by doping strategy for energy storage applications, especially supercapacitor.