Morphological and electrochemical cycling effects in MnO₂ nanostructures by 3D electron tomography

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 MnO ₂ 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. The preparation, characterization and supercapacitor application of MnO ₂ nanostructures by 3D electron tomography are studied. The electrochemical performance of MnO₂ is correlated to its surface area, determined by the morphological effect, as well as the cycling effect, determined by the formation of defective regions on the nanostructures during electrochemical cycling tests.