Hydrogen permeation of thin, free-standing Pd/Ag23% membranes before and after heat treatment in air

Free-standing Pd/Ag23 wt% membranes with five different thicknesses ranging from ∼1.3 to ∼5.0 μm were prepared by magnetron sputtering. The hydrogen permeation was determined before and after a thermal treatment in air at 300 °C. For all membranes studied, the thermal treatment resulted in enhanced permeation, and for some membranes, the hydrogen flux more than doubled. A permeance of 1.7 × 10−2 mol/m2 s Pa0.5 was observed for ∼1.3 μm thick membranes, which is one of the highest reported. Bulk diffusion was found to be the main rate-limiting step after thermal treatment in air. The permeability was quite similar for all membranes studied after this treatment, with a mean value of 2.1 × 10−8 ± 5 × 10−10 mol m/m2 s Pa0.5. Topography studies by atomic force microscopy showed that the samples thermally treated in air had higher surface roughness, larger surface area and larger surface grains than samples not heat-treated in air.