A comparative study of MnO2 and composite MnO2–Ag nanostructures prepared by a hydrothermal technique on supercapacitor applications
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Pure MnO2 and composite MnO2–Ag electrodes with four different structures were synthesized via a hydrothermal process. Tube, urchin, rod and wire/sphere-like structures were obtained from the addition of HCl, H2SO4, (NH4)2S2O8 or CO(NH2)2 reagents into potassium permanganate solutions, respectively. The crystal structure of the MnO2 particles was examined using X-ray diffraction and transmission electron microscopy, revealing an α-phase MnO2. Specific capacitance values of 74.5, 111.7, 103.4 and 204.1 F g−1 at a charge/discharge current density of 0.3 A g−1 were obtained for tube, urchin, rod and wire/sphere-like pure MnO2 structures, respectively. The wire/sphere-like structure delivered the highest specific capacitance owing to its largest specific surface area (164.60 m2 g−1). The specific capacitances were further increased to 96.6, 210.9 and 186.4 F g−1, respectively, for tube, urchin and rod-like structures after Ag addition. Additionally, the capacitance retention of the rod and wire/sphere-like composite MnO2–Ag films were also prolonged because Ag nanoparticles prevented the aggregation and/or decomposition of MnO2.
This work was financially supported through the Advanced Functional Materials Cluster of Khon Kaen University, by Nanotec KKU Excellence Center on Advanced Nanomaterials for Energy Production and Storage, by the Integrated Nanotechnology Research Center, Khon Kaen University, Thailand, by the Toray Science Foundation (TTSF), by the Thailand Research Fund (Contract No. TRG5780142), by National Research Council of Thailand (NRCT) (Contract No. 600057), by Ministry of Energy and National Science and Technology Development Agency (NSTDA) (Conctract No. P-17-50627) and the Thailand Center of Excellence in Physics (ThEP). A. Phakkhawan would like to thank the Development and Promotion of Science and Technology Talents Project (DPST) for funding and the Graduate School, Khon Kaen University for Research Scholarships they provided.
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