Mesoporous RuO2 for the next generation supercapacitors with an ultrahigh power density

The 3D mesoporous, well crystalline RuO2 film prepared via the evaporation-induced self-assembled method (EISA) successfully demonstrates the extremely high power performances (e.g., excellent capacitive behavior at 10,000 mV s-1, ultrahigh-frequency capacitive responses (the absence of a knee point in the Nyquist plot), and 2.6 MW kg-1 with an acceptable energy density of 4.6 Wh kg-1). These excellent capacitive performances were identified by means of voltammetric and electrochemical impedance spectroscopic (EIS) analyses. The mesoporous (with mean pore spacing of 18.1 nm) and crystalline nature of this film was characterized by means of the field emission scanning electron microscopy (FE-SEM), Brunaur-Emmett-Teller (BET) method, small-angle X-ray scattering (SAXRS), high-resolution transmission electron microscopy (HR-TEM), electron diffraction (ED), and X-ray diffraction (XRD) analyses. This mesoporous, well crystalline RuO2 film constrains the redox transition to the superficial region meanwhile the tailored mesoporous structure increases the electrochemically active centers, promotes the penetration of electrolytes, provides the 'proton reservoirs', and enhances the rate of electron transport simultaneously for the ultrahigh power application. The specific capacitance of this mesoporous RuO2 can be enhanced from 84 to 185 F g-1 after the microwave-assisted hydrothermal treatment.