Phase transformation of hierarchical nanobranch structure from SnO to SnO2 and its electrochemical capacitance

Hierarchical SnO2 core-shell nanobranches are produced by thermal oxidization of hierarchical SnO nanobranches that are synthesized using a vapor transport method. The SnO nanobranches with a single crystalline tetragonal structure were heat-treated at 923 K in an ambient atmosphere and completely transformed to hierarchical SnO2 nanobranches with an orthorhombic crystal structure. The SnO2 nanobranches of a polymorphism have a core-shell structure in which SnO2 phase (P-212121) is formed in the core and SnO2 phase (P-bcn) at the shell. The electrochemical capacitive properties of the SnO2 nanobranches are evaluated by cyclic voltammograms and galvanostatic charge-discharge measurements. Results show that the hierarchical SnO2 nanobranches have an excellent pseudocapacitive performance, i.e., the maximum specific capacitance of 40.5 mu F/cm(2) and long-term cycling stability up to 1000 cycles with the 8.9% loss of maximum specific capacitance. (C) 2012 Elsevier B.V. All rights reserved.