Oxidation Process and Electrochemical Properties of MoS2 Films Formed under Hydrothermal Conditions

The effect of oxidation conditions on the crystal structure, microstructural features, and electrochemical properties of molybdenum disulfide films grown under hydrothermal conditions on the surface of carbon paper substrates was studied. It was shown that additional heat treatment in an aqueous medium at 50°C leads to a partial transformation of the 1T/2H phase of MoS2 with the formation of molybdenum dioxide, whereas heat treatment in air at 350°C leads to complete oxidation of molybdenum disulfide to the α-modification of molybdenum(VI) oxide, characterized by an orthorhombic crystal structure. Scanning electron microscopy data confirm the formation of hierarchically organized films consisting of curved nanosheets in all cases. Moreover, the thickness of the nanosheets varies from 17 to 25 nm, depending on the post-processing conditions of the resulting films. X-ray elemental microanalysis allowed us to trace changes in the chemical composition of the samples as a result of their oxidation and to build maps of the element distribution across the studied material surface. Results from the electrochemical characteristics of the samples indicate that the MoS2 film exhibits the highest specific capacitance values, reaching 123 F/g, while oxidation of the material in an aqueous medium or air atmosphere leads to a decrease in this parameter.