Higher-power supercapacitor electrodes based on mesoporous manganese oxide coating on vertically aligned carbon nanofibers

Abstract

A study on the development of high-power supercapacitor materials based on formation of thick mesoporous MnO₂ shells on a highly conductive 3D template using vertically aligned carbon nanofibers (VACNFs). Coaxial manganese shells of 100 to 600 nm nominal thicknesses are sputter-coated on VACNFs and then electrochemically oxidized into rose-petal-like mesoporous MnO₂ structure. Such a 3D MnO₂/VACNF hybrid architecture provides enhanced ion diffusion throughout the whole MnO₂ shell and yields excellent current collection capability through the VACNF electrode. These two effects collectively enable faster electrochemical reactions during charge–discharge of MnO₂ in 1 M Na₂SO₄. Thick MnO₂ shells (up to 200 nm in radial thickness) can be employed, giving a specific capacitance up to 437 F g⁻¹. More importantly, supercapacitors employing such a 3D MnO₂/VACNF hybrid electrode illustrate more than one order of magnitude higher specific power than the state-of-the-art ones based on other MnO₂ structures, reaching ∼240 kW kg⁻¹, while maintaining a comparable specific energy in the range of 1 to 10 Wh kg⁻¹. This hybrid approach demonstrates the potential of 3D core–shell architectures for high-power energy storage devices.