Heat treatment driven surface segregation in Pd77Ag23 membranes and the effect on hydrogen permeability

We applied different heat treatment to commercial Pd77Ag23 membranes to promote surface segregation and measured the influence of surface segregation on hydrogen permeability. We report X-ray photoelectron spectroscopy (XPS) analysis of the surface elemental composition of the membranes. We used atomic force microscopy (AFM) to observe the surface roughness and area change. We found that surface composition varied with the method of heat treatment. The surface area of all membranes increased after heat treatment. We found that the higher the surface Pd/(Pd + Ag) ratio, the higher the hydrogen permeability. We demonstrate that surface carbon removal and surface area increase do not explain the observed permeability differences. The vacuum level during the heat treatment is crucial to promote Ag surface segregation of membranes. After exposure to hydrogen, we observed reverse segregation (Pd segregation).