Low-temperature stability of body-centered cubic PdCu membranes

Concerns about limited durability at ambient temperatures are a major obstacle for the utilization of Pd-type membranes for H-2 purification in local, on-demand H-2 production. It is clear that pure Pd membranes are not suitable for applications that involve fast regular start-up and shut-down of purification systems but knowledge remains sparse about the performance of Pd alloy membranes in such situations. Here we investigated the stability of thin-layered, supported PdCu membranes with body-centered cubic (bcc) structure between room temperature and 673 K at H-2 pressure differences Delta P-H2 up to 1 MPa. Three PdCu layers with 46-50% Pd have been prepared by alternating electrodeposition of multiple Cu and Pd layers onto metallized ceramic membranes and subsequent alloying at 673-773 K. The H-2 permeation rates of all membranes can be described by single permeation laws in the entire investigated temperature range. The nominal H-2 permeability of a Pd48Cu52 membrane amounted to 2.3 x 10(-9) mol m(-1) s(-1) Pa-0.5 at 673 K and Delta P-H2 = 100 kPa with an ideal H-2/N-2 selectivity of 3382. The H-2 fluxes and N-2 leak rates of the three membranes were not affected by cycling between room temperature and 673 K under up to 1.1 MPa H-2 which included more than a dozen H-2/N-2 exchanges at 298 K. These fluxes remained also stable through 100 h continuous operation in H-2 at that temperature. The excellent low-temperature tolerance of these membranes is attributed to the marginal hydrogen solubility in bcc PdCu alloys rendering them promising membrane materials for H-2 purification involving everyday operation at ambient temperatures.