PtRu alloy and PtRu-WO3 nanocomposite electrodes for methanol electrooxidation fabricated by a sputtering deposition method

PtRu alloy and PtRu-WO3 nanocomposite thin-film electrodes for methanol electrooxidation were fabricated by means of a sputtering method. The structural and electrochemical properties of well-defined PtRu alloy thin-film electrodes were characterized using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and electrochemical measurements. The alloy thin-film electrodes were classified as follows: Pt-based (10-40 atom % of Ru) and Ru-based (60 atom % of Ru) alloy structure. Among the electrodes formed by the sputtering method, PtRu-80, with 62 atom % Pt confirmed by XRD, showed the best catalytic activity for methanol electrooxidation. In particular, surface enrichment of Pt in the PtRu alloy thin-film electrodes, e.g. 65 atom % Pt for PtRu-80, was observed by XPS. Then, based on structural and electrochemical understanding of the PtRu alloy electrodes, PtRu-WO3 nanocomposite thin-film electrodes were formed. The well-controlled physical and (electro)chemical properties of PtRu-WO3 showed a specific current of 22 A/g at 0.45 V vs NHE, compared to that of 12 A/g for the case of conventional PtRu alloy nanosized catalyst. The homogeneous dispersion of alloy catalyst and the well-formed nanophase structure in the PtRu-WO3 would lead to an excellent catalytic electrode. In addition, the enhanced catalytic activity in the nanocomposite electrode was found to be closely related to proton transfer in tungsten oxide using in-situ electrochemical transmittance measurement.