Electrochemical Synthesis of Photoactive MoS₂

The growth of polycrystalline films and single crystals of molybdenum disulfide by electrolytic reduction of a sodium tetraborate-sodium fluoride melt containing molybdenum trioxide and sodium sulfate has been examined and physical properties of those deposits studied. Polycrystalline n-type Mos₂is readily obtained from a melt at 800°C while larger single-crystals are obtained if the melt temperature is raised to 900°C. MoS₂is a semiconductor with bandgap well matched to the solar spectrum and with unusual resistance to photoelectrochemical corrosion. Electrochemically-grown single crystals and polycrystalline films were employed as photoanodes in aqueous iodide-triiodide electrolytes under ~40 mW/cm²tungsten-halogen illumination. Open-circuit photopotentials of ~150 mV were observed for polycrystalline MoS₂. For single crystal electrolytic MoS₂an open-circuit photopotential of 210 mV and ~2 mA/cm²short circuit current were reached. The use of electrochemical methods to prepare these materials offers the advantages of relatively low growth temperatures, controlled thickness, and excellent adaptability to producing large-area films inexpensively.