Effects of heat treatment in air on hydrogen sorption over Pd–Ag and Pd–Au membrane surfaces

The effects of heat treatment in air on H2 sorption over the free-standing 25-μm cold-worked Pd–Ag25 wt% and Pd–Au10 wt% membrane surfaces were investigated. The equilibrium sorption results demonstrated that H2 solubility did not change for both Pd–Ag and Pd–Au membranes before and after air oxidation at 300 °C. The sorption kinetics data revealed a much faster H2 sorption rates for the as-received Pd–Au membrane than the as-received Pd–Ag alloy. The heat treatment in air accelerated the H2 sorption kinetics for both membranes at small H2 equilibrium pressure (EP) of 0.16 kPa. However, the oxidation enhancement extent is greater for Pd–Ag and the disparity becomes more significant when EP increases. The sorption rate enhancement for Pd–Ag membrane existed over a wide range of EPs even though the enhancement effect decreased with increasing EPs. For Pd–Au membrane, the enhancement induced by air oxidation decreased sharply when EP increased because the sorption rate is already very fast for the as-received Pd–Au alloy and there is less latitude for further improvement than Pd–Ag membrane. It is found that the variation of H2 sorption rates over membrane surfaces correlates to the change of H2 permeability. After heat treatment in air, the Pd–Ag membrane experienced a systematic increase in H2 permeability with higher permeability increase at lower pressures while there was basically no permeation increase due to air oxidation effect for the Pd–Au membrane within the pressure range of practical H2 permeation tests, which are consistent with the previously reported sorption rates hypothesis and results.

► The effects of air oxidation on H2 sorption over Pd–Ag and Pd–Au membranes. ► H2 solubility and H2 sorption rate data for Pd–Ag and Pd–Au membranes. ► The correlation of H2 sorption rate to H2 permeability caused by air oxidation.