Cyclic voltammetric formation of hollow porous γ-MnO2 microspheres as stable electrodes for high-performance supercapacitors

Cyclic voltammetry enables the fast formation of a binder-free γ-MnO2 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 MnO2, which requires chemical conversion at high temperature. Compared to amorphous MnO2, the hollow γ-MnO2 microsphere has a higher content of Mn3+, which facilitates the adsorption/desorption of electrolyte ions and redox reactions at the electrode-electrolyte interface. The hollow porous γ-MnO2 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-MnO2 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-MnO2 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.