Pd–Pt/YSZ composite membranes for hydrogen separation from synthetic water–gas shift streams

Abstract

Palladium–platinum (Pd–Pt) alloy membranes have been fabricated by sequential, electroless deposition onto porous yttria-stablized zirconia supports manufactured by Praxair, Inc. Membranes were synthesized with thicknesses of 4–12μm that contained up to 27wt% Pt. Pd–Pt alloy membranes had lower pure-gas hydrogen flux compared with pure Pd membranes of equal thickness. However, when tested at 673K under an identical synthetic water–gas shift feed gas mixture composed of H2, H2O, CO2, and CO at 689.5kPa total pressure, the Pd–Pt alloy membranes had over 25% higher hydrogen fluxes than a pure Pd membrane of similar thickness. Membrane films were analyzed after testing with SEM, EDS, and ICP-AES to corroborate membrane thickness and alloy compositions estimated by mass gain. SEM thickness estimates on membrane cross sections were similar to those estimated by mass gain. ICP-AES analysis was performed on two membranes and confirmed the composition estimated by gravimetric analysis. In five of six membranes the film composition estimated by gravimetric analysis was consistent with the surface composition estimated by EDS which indicated that the membranes had been adequately annealed.