In the past decades, the energy consumption of nonrenewable fossil fuels has been increasing, which severely threatens human life. Thus, it is very urgent to develop renewable and reliable energy storage devices with features of environmental harmlessness and low cost. High power density, excellent cycle stability, and a fast charge/discharge process make supercapacitors a promising energy device. However, the energy density of supercapacitors is still less than that of ordinary batteries. As is known to all, the electrochemical performance of supercapacitors is largely dependent on electrode materials. In this review, we firstly introduced six typical transition metal oxides (TMOs) for supercapacitor electrodes, including RuO2, Co3O4, MnO2, ZnO, XCo2O4 (X = Mn, Cu, Ni), and AMoO4 (A = Co, Mn, Ni, Zn). Secondly, the problems of these TMOs in practical application are presented and the corresponding feasible solutions are clarified. Then, we summarize the latest developments of the six TMOs for supercapacitor electrodes. Finally, we discuss the developing trend of supercapacitors and give some recommendations for the future of supercapacitors.
Ni-metal–organic framework
(MOF)/nano carbon (NC) electrode
materials were synthesized by a one-step hydrothermal method. The
prepared Ni-MOF/NC presented in the form of NC distributed uniformly
on the Ni-MOF sheets, which effectively increased the specific surface
area of the material and the rate of redox reaction. The Ni-MOF/NC
electrode delivered 828 F/g at 1 A/g. In addition, the asymmetric
supercapacitor (ASC) assembled by Ni-MOF/NC and active carbon retained
100% of specific capacitance after 5000 cycles. Furthermore, the ASC
delivered energy density of 23.84 W h/kg at 849.74 W/g.
The flower-like NiCo MOF prepared by a hydrothermal has a specific capacitance of 927.1 F g−1 at 1 A g−1 and a capacitance retention of 69.7% from 1 A g−1 to 10 A g−1, showing excellent electrochemical performance.
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