Effect of the KMnO₄ concentration on the structure and electrochemical behavior of MnO₂

Various MnO₂ structures have been synthesized in this study by a facile method through the manipulation of KMnO₄ concentration. The effect of KMnO₄ concentration on the structure and morphology has been thoroughly investigated by X-ray powder diffraction, field-emission scanning electron microscopy, and nitrogen adsorption–desorption measurements. Birnessite-type MnO₂ flower-like microsphere can be obtained at a lower concentration, while α-MnO₂ nanorods can be obtained at a higher concentration. By increasing the KMnO₄ concentration further, α-MnO₂ nanorods can assemble into urchin-like microspheres and spherical aggregates. The possible formation mechanism based on the experimental results has been proposed to understand their growth procedures. The electrochemical properties of the synthesized materials evaluated by cyclic voltammetry and constant-current charge–discharge cycling techniques are dependent on their pore size distribution and nanostructures. Birnessite-type MnO₂ microsphere showed excellent capacitive behavior with a maximum specific capacitance of 185 F g⁻¹.