MnO₂ Nanoparticles Prepared by Alternating Monopolar Arrangement Electrolysis and Their Electrochemical Performances

Manganese dioxide nanoparticles have been successfully synthesized by the electrolysis method using 4-pairs carbon electrode in the alternating monopolar arrangement. The advantage of the arrangement is a significant increase in the product yield compared to the single pair electrodes. KMnO₄ solution in pH 0.2 and 9 were used as precursor and electrolyzed for thirty minutes at a temperature of 60 °C. The generated particles resulted from electrolysis in pH 0.2 (MnO₂-A) and in pH 9 (MnO₂-B) were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and nitrogen adsorption-desorption isotherms to examine their crystallinity, morphology, and the specific surface area. The α-MnO₂ was observed for MnO₂-A particles and amorphous for MnO₂-B particles. The particles size of MnO₂-A was larger than that of MnO₂-B with the specific surface areas of 396 and 98 m²/g, respectively. The higher surface area of MnO₂-A corresponding to the channel pore of short rod-like morphology. On the other hand, MnO₂-B contributed to the spherical particles. The measurements of cyclic voltammetry (CV) were also carried out to measure their specific capacitances and their performance for oxygen reduction reaction (ORR) electrocatalyst. MnO₂-A exhibited higher specific capacitance of 13.57 F/g compared to MnO₂-B that only had 3.62 F/g. In addition, MnO₂-A also gave better performance as ORR electrocatalyst measured in O₂-saturated 0.6 M KOH resulted in 2.69 transferred electron number per oxygen molecule.