Sequential electrodeposition of Mo at Pt and PtRu methanol oxidation catalyst particles on HOPG surfaces

Sequential electrodeposition methods were used to prepare PtMo and PtRuMo methanol electrocatalyst particles on previously activated highly oriented pyrolytic graphite (HOPG) substrate. The influences of Mo and Ru concentration content on the particles were studied by electrochemistry and surface science techniques. Catalysts deposited by the sequential method showed better catalytic behavior when compared with simultaneous deposition of the same binary and ternary systems. Morphological and microscopic characterization, by scanning electron microscopy (SEM) and atomic force microscopy (AFM), showed that, in general, the deposits are clusters of aggregated nanoparticles. Scanning tunneling microscopy (STM) showed that the tops of these clusters are from 5 to 10 nm in diameter. These clusters were heterogeneous and dispersed on the HOPG surface. X-ray photoelectron spectroscopy (XPS) of HOPG/PtMo electrodes showed the presence of the different molybdenum oxidation states. When Mo was deposited with PtRu, Mo did not remain as the same species, and Ru was present as a metal. Cyclic voltammetry and chronoamperometry showed that methanol oxidation current densities and mass activity were enhanced for the PtRu and PtRuMo electrodes when compared to pure Pt nanoclusters on HOPG electrodes. The sequential electrodeposition method, with optimal Mo and Ru concentrations, will produce catalysts with highly electrocatalytic surfaces and high dispersion.