Investigation of the photoelectrochemical properties of layered manganese oxide

Abstract

Due to the greenhouse effect and limited amount of fossil fuels, the need for a new, renewable, and clean energy source is becoming more important for the near future. Among metal–oxide semiconductors, instead of its photoelectrochemical properties, manganese oxide is better known for its electrochemical water-splitting properties. However, there have been reports on studies of the photoelectrochemical water-splitting ability of manganese oxide. A number of aspects of manganese oxide require further investigation: for instance the photocurrent-generation mechanism, the effect of the electrolyte solution composition, careful study of the excitation wavelength and the applied bias potential and the band structure of layered manganese oxide. The photoelectrochemical properties of layered manganese oxide were exhaustively studied and the effects of the applied bias potential, the solution composition, the presence and the absence of oxygen, and the excitation wavelength were investigated. The experiments showed that under different conditions manganese oxide shows reductive and oxidative photocurrent. Furthermore, manganese oxide was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The experiments showed that during experiments and by application of an 800 mV bias potential, because of electrochemical oxidation of manganese and changing its oxidation state, the level of disorder between layers in the crystal structure of birnessite decreases. This alteration in the structure and morphology has a significant effect on the observed photoelectrochemical behaviour of the manganese oxide coated gold electrode, which results in a reductive photocurrent in lower potential and longer wavelength ranges. Furthermore, depleting the oxygen in the electrolyte solution also has a significant impact on the observed photoelectrochemical behaviour of the manganese oxide coated gold electrode and results in a reductive photocurrent.