Hydrogen transport in palladium membranes

The hydrogen flux in palladium membranes acquired from different vendors has been measured as a function of membrane thickness, temperature and feed (pure H2) pressure p1, with permeate (pure H2) pressure p2 fixed at 1 atm. Palladium foils 12.5, 25 and 47 µm thick were studied at 75–500°C and p1 values of 3.4–6.8 atm. Arrhenius plots of flux, measured with p1 fixed, include a peak within an intermediate temperature range, and different activation energies in the low and high temperature ranges. The peak may be explained by palladium hydride’s "–$ phase transition, which, at intermediate temperatures, takes place at hydrogen activities between those at the respective membrane surfaces. The two activation energies apparently reflect different rate-controlling processes: bulk diffusion at high temperatures and surface phenomena at low temperatures.