Hydrogen separation by Pd alloy composite membranes: introduction of diffusion barrier

Abstract Thin (less than 2 μm thickness) and pinhole-free palladium–copper (Pd–Cu) alloy composite membranes with a diffusion barrier have been fabricated on mesoporous stainless steel supports by vacuum electrodeposition. The deposition film was fabricated by multilayer coating and diffusion treatment and the formation of Pd–Cu alloys was achieved by annealing the as-deposited membranes at 723 K in nitrogen atmosphere. To improve the structural stability of Pd alloy/Ni–SUS composite membranes, a thin intermediate layer of silica by sol–gel method was introduced as a diffusion barrier between Pd–Cu active layer and a modified SUS substrate. The composition and phase structures of the alloy film were studied by energy dispersive electronic analysis (EDS) and X-ray diffractometry (XRD); the typical Pd–Cu plating had composition of 63% Pd and 37% Cu and the atomic inter-diffusion of Pd and Cu resulted in Pd–Cu alloys in a fcc structure. The electron probe microanalyzer (EPMA) profiling analysis indicated that the improved membranes were structurally stable. The Pd–Cu alloy composite membrane obtained in this study yielded excellent separation performance for hydrogen: hydrogen permeance of 2.5×10 −2  cm 3 /cm 2  cmHg s and hydrogen/nitrogen (H 2 /N 2 ) selectivity was above 70 000 at 723 K.