Enhanced capacitive properties of all-metal-oxide-nanoparticle-based asymmetric supercapacitors

The major problem of transition metal oxide (TMO)-based supercapacitors is their low specific energy (E _sp) due to the poor electrical conductivity of the TMO electrodes and narrow operating voltage window. To solve these limitations simultaneously, we propose asymmetric supercapacitors (ASCs) consisting of two composite TMO electrodes working in different potential ranges. Titanium dioxide (TiO₂) nanoparticle (NP)-incorporated iron oxide (Fe₂O₃) and manganese oxide (MnO₂) NPs were used as electrode materials covering the negative and positive potential window, respectively. The specific capacitance (C _sp) of this asymmetric TiO₂-Fe₂O₃‖TiO₂-MnO₂ supercapacitor is comparable to that of the symmetric TiO₂-MnO₂‖TiO₂-MnO₂ supercapacitor. However, the ASC can operate over a doubly extended voltage range, which resulted in a significant enhancement in the specific energy of the device. The E _sp value of the ASC at a specific power of 1000 W kg^-1 is 48.6 W h kg^-1, which is 34.1 and 8.1 times, respectively, larger than that of the two symmetric devices.