Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of Water

Different manganese oxide phases were prepared as thin films to elucidate their structure–function relationship with respect to oxygen evolution in the process of water splitting. For this purpose, amorphous MnOx films anodically deposited on F:SnO2/glass and annealed at different temperatures (to improve film adherence and crystallinity) were tested in neutral and alkaline electrolytes. Differential electrochemical mass spectroscopy showed that the anodic current correlated well with the onset of the expected oxygen evolution, where in 1 M KOH, the anodic current of crystalline α-Mn2O3 films was determined to onset at an overpotential (η) of 170 mVRHE (at J = 0.1 mA/cm2) with current densities of ca. 20 mA/cm2 at η = 570 mVRHE. Amorphous MnOx films heated at 573 K (MnOx-573 K) were found to improve their adherence to F:SnO2/glass substrate after heat treatment with a slight crystallization detected by Raman spectroscopy. The onset of water oxidation of MnOx-573 K films was identified at η = 230 mVRHE (at...