Restricted and epitaxial growth of MnO2-x nano-flowers in/out carbon nanofibers for long-term cycling stability supercapacitor electrodes

Carbon nanofibers (CFs) have been widely applied as electrodes for energy storage devices owing to the features of increased contact area between electrodes and electrolyte, and shortened transmission route of electrons. However, the poor electrochemical activity and severe waste of space hinder their further application as supercapacitors electrodes. In this work, MnO2−x nanoflowers restricted and epitaxial growth in/out carbon nanofibers (MnO2/MnO@CF) were prepared as excellent electrode materials for supercapacitors. With the synergistic effect of uniquely designed structure and the introduction of MnO and MnO2 nanoflowers, the prepared interconnected MnO2/MnO@CF electrodes demonstrated satisfactory electrochemical performance. Furthermore, the MnO2/MnO@CF//activated carbon (AC) asymmetric supercapacitor offered an outstanding long-term cycle stability. Besides, kinetic analysis of MnO2/MnO@CF-90 was conducted and the diffusion-dominated storage mechanism was well-revealed. This concept of "internal and external simultaneous decoration" with different valence states of manganese oxides was proven to improve the electrochemical performance of carbon nanofibers, which could be generalized to the preparation and performance improvement of other fiber-based electrodes.