Electrochemical preparation of catalysts on HOPG substrate: A morphological and electrocatalytic study

Platinum is extensively used for different processes; many studies have been performed to improve the CO tolerance of this catalyst, combining Pt with other metals. This work focuses on fundamental studies at a microscale level of Pt combined with Ru and Mo supported on a substrate of well-known properties and easy handling like is Highly Oriented Pyrolytic Graphite (HOPG). Pt was supported on HOPG substrate by electrochemical techniques, introducing metals: Ru and Mo by sequential and simultaneous methods resulting in binary PtRu, PtMo and ternary PtRuMo systems. These systems were studied through electrochemical (voltammetry) and morphological characterization (SEM, SPM and XPS) combined with electrocatalytic tests toward methanol electrooxidation by cyclic voltammetry and chronoamperometry, to evaluate the possible morphologic changes and relate them with the catalytic activity.; Four different techniques (sweep potential, step and sweep potential, step potential and square wave) were used to improve the morphology and catalytic behavior of Pt. The Step and sweep potential technique showed better morphological and catalytic characteristics for Pt electrodeposition and this technique was used for the addition of Ru and Mo. The PtRu and PtRuMo electrocatalysts prepared on HOPG were made by either sequential and simultaneous electrodeposition methods and PtMo was prepared using sequential electrodeposition methods.; The voltammetric behavior of electrodeposits of PtRu, PtMo and PtRuMo in 0.5 M aqueous sulfuric acid was compared to that of Pt electrodeposits on HOPG in the hydrogen electroadsorption-desorption. Morphological and microscopic surface characterizations through SEM and SPM have in general shown a formation of particles with varying shapes and sizes, where the deposits consist of a number of aggregates. For sequentially produced PtRu, PtMo, PtRuMo electrodeposits, XPS and voltammetry data indicate an irregular distribution of the active materials and a non-homogeneous surface. The electrocatalytic activity of these electrodes for the oxidation of methanol in 0.5 M aqueous sulfuric acid showed better behavior for the system PtRuMo with respect to Pt. Lower electrocatalytic efficiency was found for PtRuMo and PtRu electrodes produced by simultaneous electrodeposition. Effect of various concentrations of Mo in Pt/HOPG gave slightly enhanced performance compared to a pure Pt electrode, but the performance was still inferior to that exhibited by the PtRu and PtRuMo system.; Cyclic voltammetry and chronoamperometry have been used to measure catalytic effects of these particles for methanol electrooxidation, showing that the effect of small amounts of Ru and Mo in Pt exhibited enhanced performance compared to the Pt/HOPG electrode. It is known that Ru provides OH species, and Mo, due to the rapid changes in the oxidation states forms Mo oxy-hydroxide species. The presence of such species could be the reason for the enhanced catalytic activity.; XPS analysis for the PtRuMo system showed the formation of different species with respect to the binary catalysts studied.; The PtRuMo deposit was characterized by X-ray diffraction and was compared to the X-ray diffraction obtained for Pt, PtRu and PtMo catalysts electrodeposited on HOPG substrates. In general this showed a slightly widening of the Pt peak when Ru and Mo are added compared to Pt alone.