Characterization of spray pyrolyzed manganese oxide powders deposited by electrophoretic deposition technique

Nanocrystalline manganese oxide powders were prepared by spray pyrolysis (SP) from manganese acetate solution at 400 °C. The as-obtained powders were subsequently coated onto graphite substrates via an electrophoretic deposition technique (EPD). The as-prepared powders were examined by transmission electron microscopy (TEM), X-ray diffractometry (XRD), synchrotron X-ray absorption spectroscopy (XAS); the coatings were further examined by cycling voltammetry (CV). Experimental results showed that manganese oxide powders prepared at 400 °C were hollow spherical particles with fractured shells and possessed high surface area. CV examination showed that the as-deposited coatings also exhibited the highest specific capacitance of 275 F/g. After hundreds of CV cycles, the specific capacitance decreased to 234 F/g, which was still comparable to values reported in the literature. Structural investigation by TEM and XRD revealed that the as-deposited coatings exhibited Mn₃O₄ phase with amorphous-like structure. While synchrotron XAS results showed that the manganese had a valence of + 2.67, it was transited into tetravalent manganese after cyclic voltammetry.