High pseudocapacitance of MnO2nanoparticles in graphitic disordered mesoporous carbon at high scan rates

Abstract

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.