Surface properties of PdAu and PdNi alloys under dynamic conditions: NAP-XPS study

Abstract

Electroless-deposited PdAu and PdNi alloy samples were analyzed using near-ambient X-ray photoelectron Spectroscopy (NAP-XPS) under H2, CO, and CO2-containing streams. Gold enrichment in the near-surface region was evidenced in the PdAu sample under all the analyzed conditions, while palladium increment to the surface was observed in the PdNi alloy. The appearance of a new contribution on the Pd 3d core-level region evidenced the formation of PdHx species on the surface. Competitive CO adsorption and the formation of CHx species at the surface led to the partial blocking of hydrogen adsorption sites, thereby decreasing the PdHx formation. Methane production was detected under CO/H2 and CO2/H2 mixtures in both PdAu and PdNi alloy samples. Our findings demonstrate that both competitive adsorption and the formation of CHx or carbide species on the surface of PdAu and PdNi alloys can negatively influence hydrogen permeation through Pd-based membranes.