Specific permeabilities and diffusion constants for H have been measured for a series of Pd-Al alloy membranes using a novel method for activating the membranes, i.e., partial internal oxidization. If the percent internal oxidation is small relative to the membrane thickness, the diffusion will take place essentially through the unoxidized alloys. The H diffusion constants decrease almost linearly with atom fraction Al and the activation energies increase from 23.2 kJ/mol H (X-A1, = 0) to 25.4 kJ/mol H (X-A1 = 0.10). It is shown that the partially oxidized alloys are more resistant to CO poisoning than are the corresponding unoxidized alloys and pure Pd. Thus, the partially internally oxidized alloy membranes have two advantages as H-2 purification membranes: (i) they are more reproducible than Pd or the unoxidized Pd-Al membranes; and (ii) they are more resistant to CO(g), which is a common catalytic poison for Pd. (c) 2005 Elsevier B.V. All rights reserved.