Investigation of Hydrothermally Synthesized Ruthenium Selenides as Methanol-Tolerant Oxygen Reduction Catalysts

Ruthenium selenides (RuSex) with Ru and Se molar ratios (Ru/Se), 1: 1 and 1: 2, have been prepared by the hydrothermal method using ruthenium (III) chloride and selenium powder as precursors. Structural and electrochemical characterizations of materials were performed by X-ray diffraction, scanning and transmission electron microscopes, energy-dispersive X-ray analysis, and cyclic and linear sweep voltammetries. The study confirmed that the hydrothermal method produces the nanocrystalline pyrite-type cubic RuSe2 with both Ru/Se ratios. The catalyst material was porous with the average particles size <10 nm. Both the catalysts were highly active for the oxygen reduction reaction (ORR), on the contrary, they were inactive toward the methanol electrooxidation in 0.1 M HClO4. However, RuSex obtained with x=1 is found to be more ORR active than one obtained with x=2. Results of the ORR study performed by a rotating disk electrode in 0.1 M HClO4 favor a four-electron pathway from O-2 to H2O.