Simple Formation of Nanostructured Molybdenum Disulfide Thin Films by Electrodeposition

Nanostructured molybdenum disulfide thin films were deposited on various substrates by direct current (DC) electrolysis form aqueous electrolyte containing molybdate and sulfide ions. Post deposition annealing at higher temperatures in the range 450–700°C transformed the as-deposited amorphous films to nanocrystalline structure. High temperature X-ray diffraction studies clearly recorded the crystal structure transformations associated with grain growth with increase in annealing temperature. Surface morphology investigations revealed featureless structure in case of as-deposited surface; upon annealing it converts into a surface with protruding nanotubes, nanorods, or dumbbell shape nanofeatures. UV-visible and FTIR spectra confirmed about the presence of Mo-S bonding in the deposited films. Transmission electron microscopic examination showed that the annealed MoS2 films consist of nanoballs, nanoribbons, and multiple wall nanotubes. 1. Introduction Molybdenum disulfide, MoS2, that naturally occurs as molybdenite has layered hexagonal packed structure consisting of –S–Mo–S– sheets stacked one after another by van der Waals interactions. Because of its layered structure, it has got very good lubrication properties due to shearing of layers under the application of normal load. It is perhaps most well-known heterogeneous catalyst in industry for hydrodesulfurization (HDS) of petroleum [1]. Apart from these, due to suitable electron band-gap (~1.7 ev), there is an upsurge interest on MoS2 solar cell [2] and solar hydrogen production materials [3–5]. Recently DFT calculations [6] showed that in its nanoparticulate form, MoS2 has demonstrated as promising and inexpensive alternative to platinum for electrochemical and photochemical production of hydrogen from water [7, 8]. It emphasized that presence of edges of S–Mo–S sheet is the active sites; in particular the Mo-edges have the least energy requirement for bonding hydrogen [7–10]. However, precise molecular structure and modes of action of these sites remain unresolved. Therefore, the synthesis of MoS2 nanoparticulate or nanostructured form having maximum edges of S–Mo–S sheets is of recent investigations concern. Several synthetic approaches like wet inorganic solvent route, template-based, and chemical vapor deposition techniques have been followed [9–15] to prepare such nano-particulate or nanostructured MoS2 in order to maximize the sulfide edge effect on hydrogen generation. Synthesis of such MoS2 nanoparticles or nanostructured forms via stable amorphous precursor followed by crystallization could