Electrochemistry and photochemistry of MoS2 layer crystals. I

The chemical and photochemical behaviour of MoS2-van der Waals surfaces in contact with an aqueous electrolyte has been investigated by means of electrochemical techniques. The covalent bonding character of this layer crystal and a molybdenum dz2-band which is split off from the 4d molybdenum conduction band and overlaps the sulfur 3p valence band give rise to reaction behaviour which is very different from that found with polar metal-sulfide compounds: sulfate and not molecular sulfur is the main product of the electrochemical and photochemical oxidation of MoS2 which occurs as p−, n−, or intrinsic semiconductor material. A parallel photochemical liberation of molecular oxygen could be traced on freshly prepared surfaces by means of polarographic techniques. The quantum efficiency for the photoelectrochemical reaction with water in the visible spectral range approaches 100% if a positive electrode potential of 2 V is applied. Several electron-transfer reactions were examined and the interrelation between d-band structure of the layer sulfide and some of its electrochemical behaviour is discussed.