Low-temperature stability of body-centered cubic PdCu membranes

Abstract

Concerns about limited durability at ambient temperatures are a major obstacle for the utilization of Pd-type membranes for H2 purification in local, on-demand H2 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 673K at H2 pressure differences ΔPH2 up to 1MPa. 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 673–773K. The H2 permeation rates of all membranes can be described by single permeation laws in the entire investigated temperature range. The nominal H2 permeability of a Pd48Cu52 membrane amounted to 2.3 × 10−9molm−1s−1Pa−0.5 at 673K and ΔPH2 = 100kPa with an ideal H2/N2 selectivity of 3382. The H2 fluxes and N2 leak rates of the three membranes were not affected by cycling between room temperature and 673K under up to 1.1MPa H2 which included more than a dozen H2/N2 exchanges at 298K. These fluxes remained also stable through 100h continuous operation in H2 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 H2 purification involving everyday operation at ambient temperatures.