Phase and microstructure control of electrodeposited Manganese Oxide with enhanced optical properties

Mn3O4 and Mn2O3 were synthesized by potentiostatic electrodeposition from a de-aerated manganese acetate and sodium sulfate electrolytic bath, followed by annealing. The electrodeposition parameters (including applied potential, precursor concentration, pH, temperature) and the thermal treatment conditions were investigated to obtain the best control over microstructure and stoichiometry of manganese oxides. We found that the applied voltage is the key parameter affecting the valence state of initial amorphous manganese while the thermal treatment leads to crystallization and tuning of optical properties without substantially changing the morphology. The as-electrodeposited manganese oxides are X-rays amorphous, while two different crystalline phases, Mn3O4 and Mn2O3, were obtained after the thermal treatment depending on the applied voltage. Through the analysis of TEM cross section images, a fiber-like growth was observed for Mn3O4, while Mn2O3 presented a less porous-more compact microstructure. The optical properties were investigated, resulting in an enhancement in the charge separation properties of the thermally treated manganese oxides, reflected by nearly a 40 % reduction in the photoluminescence peak intensity. We believe that these finding will be useful in the future development of environmental friendly manganese oxide-based photoelectrochemical systems.

Automated summary

In this study, Mn3O4 and Mn2O3 were synthesized through electrodeposition and thermal treatment. The effects of different parameters on the structure and optical properties of manganese oxides were investigated, and it was found that the applied voltage played a key role in controlling the valence state of initial amorphous manganese.