The compound semiconductor RuS 2 , known as mineral laurite, has been investigated as a potential (photo)electrochemically active anode material for the oxygen evolution in the process of (photo)electrolytic water splitting. The contribution describes for the first time the preparation of RuS 2 thin films deposited on (100)-and (111)-oriented FeS 2 (pyrite) substrates using reactive magnetron sputtering. The epitaxial growth of 60 nm thick films was confirmed by X-ray diffractometry, texture measurements and the evaluation of cross section transmission electron micrographs. By optical reflectance spectroscopy and Seebeck coefficient measurements a direct band gap of 1.9 eV and p-type conductivity could be determined. Due to the modest electrochemical stability of the epitaxial layers in electrochemical investigations, polycrystalline films of laurite were also deposited on Ti sheets and Si wafers. As a function of grain size, [S]:[Ru] ratio and grain orientation highest activity towards oxygen evolution was found when the conditions were fulfilled that the layer composition was close to stoichiometry and increased particle sizes showed a strong textured in the grains. Some structural and chemical properties argue for the (100) surface as catalytically active and stable layer compared to other surfaces.
Crystalline RuS(2) layers were prepared on titanium sheets by reactive magnetron sputtering using a metallic ruthenium target and a H(2)S-Ar mixture as process gas. The ability of these layers for the electrooxidation of water (OER) was investigated by differential electrochemical mass spectrometry (DEMS) in 0.5 M H(2)SO(4) electrolyte. It was observed that the activity for water oxidation is increased with increasing temperature of the titanium substrate during the sputter deposition process whereas a competitive corrosion process is diminished. The reason for this effect seems to be a better crystallinity of these layers at higher substrate temperatures as it is proved by XRD analysis. In contrast to RuS(2) single crystals no photo effect could be observed on the sputtered layers under illumination with a tungsten lamp. Time resolved microwave conductivity analysis indicates the presence of mobile charge carriers after illumination but apparently these cannot participate in the electrooxidation of water.
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