A high throughput synthetic and screening methodology has been applied to the study of the Hydrogen Evolution Reaction (HER) and Hydrogen Oxidation Reaction (HOR) activities of PdAu thin film alloy surfaces. A compositional gradient method has been used to produce non-equilibrium surfaces of PdAu solid solution alloys. XPS shows surface compositions for these un-annealed alloys to be the same as the bulk, in contrast to the observed and expected behaviour of annealed alloys. The surface redox behaviour of the alloys provides direct evidence for the existence of Pd ensembles with distinctive surface chemistry dominating the oxygen interaction at intermediate alloy compositions. CO stripping voltammetry indicates that alloying of Pd with Au results in a strong poisoning of CO adsorption with the exception of CO adsorbed on Pd monomers. The compositional dependence of the HER and HOR activities is strongly correlated on the alloy surfaces, with a maximum in geometric activity observed at 60 at% Au, corresponding to a maximum in specific activity at 70 at% Au, for both reactions. This activity is associated with Pd poor ensembles. There is some evidence that while the Pd monomer catalyses the HER, HOR is not sustained at compositions where the monomer is present.

Model carbon supported Pt and Pd electrocatalysts have been prepared using a high-throughput physical vapor deposition method. For Pt, metal particle sizes are controlled between 1.5-5.5 nm over 100 electrodes of an electrochemical screening chip, allowing the oxygen reduction reaction (ORR) activity of the catalysts to be determined simultaneously. The ORR-specific current density is observed to increase with increasing particle diameter up to approximately 4 nm, at which point the activity begins to level off. The reduction in ORR activity for particles below 4 nm is accompanied by a concomitant increase in the overpotential for surface reduction. The resulting mass activity exhibits a maximum for particles with diameters of approximately 3.5 nm. These results are consistent with results published recently for high area carbon-supported Pt catalysts. For Pd particles, both the specific current density and the mass-specific activity for the ORR are observed to increase with increasing particle diameter, with no distinct optimum observed. The implications for the optimization of Pt- or Pd-based ORR catalysts for proton exchange membrane fuel cell (PEMFC) applications are discussed.

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Thin film alloys of PdBi have been synthesised using a high throughput physical vapour deposition method to produce compositional gradients of PdBi alloys. XPS indicates that for the non-equilibrated thin films, the surface composition is the same as the bulk, and core level shifts reflect the inter-metallic interaction between the component metals. Hydrogen absorption is hindered in the PdBi alloys, and at a composition of 70 at.% bismuth, the aBi 2 Pd bulk alloy phase is identified in XRD. This phase exhibits a maximum in the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) electrocatalytic activity. The increased activity of the alloy can be understood in terms of the Pd d-band density of states, and a concomitant increase in the binding energy of hydrogen. There is a strong correlation between the HER and HOR activity as a function of composition across the complete range of alloys. The potential of using the aBi 2 Pd bulk inter-metallic phase at the anode of PEM fuel cells is briefly discussed.