Diffusion of H through Pd–Y alloy membranes

Abstract

Fick's diffusion constants, DH, for H in Pd–Y alloys decrease with the increase of atom fraction Y, XY, for the alloys investigated here (XY≤0.095), however, the H permeabilities increase because the H2solubility increase is greater than the decrease of the diffusion constant. DH values have been measured for some of the Pd–Y alloys over a large range of H contents and, for several alloys, minima appear in plots of RTlnDH against rup arising from non-ideality, i.e., thermodynamic factor ≠1, where rup=H-to-metal mol ratio at the upstream surface of the membrane and rdown=0. Concentration independent diffusion constants have been derived from the concentration-dependent ones and the thermodynamic factor.The effect of CO on the permeation of H through Pd–Y membranes has been determined and compared to the effect of CO on the permeability of a Pd0.77Ag0.23alloy. The poisoning effect of CO is either greater or similar for the un-oxidized Pd0.77Ag0.23alloy membranes and the internally oxidized Pd–Y alloy membranes, although any differences are small.