High pseudocapacitance of MnO2 nanoparticles in graphitic disordered mesoporous carbon at high scan rates

Nanocomposites composed of MnO2 and graphitic disordered mesoporous carbon (MnO2/C) were synthesized for high total specific capacitance and redox pseudocapacitance (C-MnO2) at high scan rates up to 200 mV s(-1). High resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray spectroscopy (EDX) demonstrated that MnO2 nanodomains were highly dispersed throughout the mesoporous carbon structure. According to HRTEM and X-ray diffraction (XRD), the MnO2 domains are shown to be primarily amorphous and less than 5 nm in size. For these composites in aqueous 1 M Na2SO4 electrolyte, C-MnO2 reached 500 F/g(MnO2) at 2 mV s(-1) for 8.8 wt% MnO2. A capacitance fade of only 20% over a 100-fold change in scan rate was observed for a high loading of 35 wt% MnO2 with a C-MnO2 of 310 F/g(MnO2) at the highest scan rate of 200 mV s(-1). The high electronic conductivity of the graphitic 3D disordered mesoporous carbon support in conjunction with the thin MnO2 nanodomains facilitate rapid electron and ion transport offering the potential of improved high power density energy storage pseudocapacitors.