General synthesis of hierarchical C/MOx@MnO2 (M=Mn, Cu, Co) composite nanofibers for high-performance supercapacitor electrodes.

Improving the conductivity and specific surface area of electrospun carbon nanofibers (CNFs) is beneficial to a rapid realization of their applications in energy storage field. Here, a series of one-dimensional C/MOx (M=Mn, Cu, Co) nanostructures are first prepared by a simple two-step process consisting of electrospinning and thermal treatment. The presence of low-valence MOx enhances the porosity and conductivity of nanocomposites to some extent through expanding graphitic domains or mixing metallic Cu into the CNF substrates. Next, the C/MOx frameworks are coated with MnO2 nanosheets/nanowhiskers (C/MOx@MnO2), during which process the low-valence MOx can partly reduce KMnO4 so as to mitigate the consumption of CNFs. When used as active materials for supercapacitor electrodes, the obtained C/MOx@MnO2 exhibit excellent electrochemical performances in comparison with the common CNFs@MnO2 (CM) core-shell electrode due to the combination of desired functions of the individual components and the introduction of extra synergistic effect. It is believed that these results will provide an alternative way to further increase the capacitive properties of CNFs- or metal oxide-based nanomaterials and potentially stimulate the investigation on other kinds of C/MOx composite nanostructures for various applications.