Measurement and modeling of hydrogen transport through high-flux Pd membranes

The permeability of H2-selective palladium membranes fabricated with microsystem technology has been studied. The permeation experiments have been carried out at temperatures between 623 and 873 K at H2 feed partial pressures of 0.2–1.0 bar. At 823 K, a permeance based on the free membrane area of 18 mol H2/m2 s bar0.58 has been measured for a Pd membrane with a thickness of 0.5 μm. From the permeation experiments the rate determining transport step and the stability of the membranes have been determined. At 873 K the H2/He selectivity decreases rapidly, indicating the formation of pinholes at higher temperatures. From a combination of experiments and computer simulations the limiting transport step has been determined to be H-atom diffusion through the membrane at elevated temperatures and H2 surface reactions at the retentate side at lower temperatures.