Abstract
In this study, MnO2 nanostructures with well-controlled morphology and crystal phase are successfully prepared by chemical synthesis, and characterized by three-dimensional electron tomography for use as supercapacitor electrode materials. The growth process of the various MnO2 nanostructures is revealed in detail, and correlated to their electrochemical performance as supercapacitor materials. The specific capacitance of MnO2 electrodes is found to be strongly correlated with the inner morphology and crystal phase of the MnO2 nanostructures. Furthermore, it is demonstrated that the increased capacity with electrochemical cycling of the materials is due to the formation of defective regions embedded in the MnO2 nanostructures; these regions form during electrochemical cycling of the electrodes, resulting in increased porosity, surface area, and consequently, increased electrochemical capacity.