Cyclic voltammetric formation of hollow porous γ-MnO2 microspheres as stable electrodes for high-performance supercapacitors
Mao-Sung Wu, Li-Rong Hong
Abstract
Cyclic voltammetry enables the fast formation of a binder-free γ-MnO 2 electrode at room temperature , which features hollow porous microspheres with electrically connected networks. This process leads to a significantly improved supercapacitive performance compared to conventional binder-based MnO 2 , which requires chemical conversion at high temperature. Compared to amorphous MnO 2 , the hollow γ-MnO 2 microsphere has a higher content of Mn 3+ , which facilitates the adsorption/desorption of electrolyte ions and redox reactions at the electrode-electrolyte interface. The hollow porous γ-MnO 2 exhibits a high specific capacitance of 405 F g −1 at 1 A g −1 and demonstrates excellent rate capability, with a specific capacitance of 250 F g −1 at 50 A g −1 . Remarkably, the specific capacitance remains almost unchanged after 3000 charge/discharge cycles at 10 A g −1 . The electrochemical impedance spectroscopy confirms that the γ-MnO 2 electrode with hollow porous microspheres outperforms its counterpart, due to its shorter dielectric relaxation time (1.4 s), lower contact resistance, and smaller charge and mass transfer resistances. The novel binder-free γ-MnO 2 electrode with hollow porous microspheres provides electrically connected networks, large active sites, and rapid ion transport within the pores and crystal tunnels. This enables faster and more efficient charge storage.