Hydrogen Evolution and Hydrogen Oxidation on Palladium Bismuth Alloys

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 alpha Bi2Pd 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 alpha Bi2Pd bulk inter-metallic phase at the anode of PEM fuel cells is briefly discussed.