Heterogeneous manganese oxide-encased carbon nanocomposite fibers for high performance pseudocapacitors

The integration of transition metal oxide nanocrystals and one-dimensional (1D) conducting carbon structures to generate their hybrids can create unpredictable new physical and chemical properties in comparison with single phase components. Here we report the fabrication of heterogeneous MnO nanocrystal (NC)-encased hierarchical carbon nanocomposite fibers (MCNFs) via a novel and large-scale Forcespinning followed by low temperature carbonization. Manganese nitrate containing polyvinylpyrrolidone (PVP) polymeric fiber was carbonized at relatively low temperature, i.e. 500°C due to oxidant Mn ²⁺ cations. Different inward and outward ionic diffusion rates of Mn²⁺ cations concurrently result in congregating MnO NCs near the surface region of the nanocomposites during thermolysis. After anodic and cyclic voltammetric electrochemical oxidations, in situ phase transformation from electrochemically inactive MnO NCs to pseudocapacitive MnO_x counterparts occurs, which yields a MnO_x NC/carbon hybrid fiber network with MnO_x NC-enriched functional surface. These NCs are accessible to aqueous electrolyte ions for Faradic redox reactions. Therefore these unique nanocomposites demonstrate a promising potential as pseudocapacitive electrode materials.