Electroless plating synthesis, characterization and permeation properties of Pd–Cu membranes supported on ZrO2 modified porous stainless steel

Thin Pd–Cu membranes were prepared by electroless plating technique on porous stainless steel (PSS) disks coated with a mesoporous palladium impregnated zirconia intermediate layer. This intermediate layer provides seeds for electroless plating growth of Pd–Cu film during synthesis and serves as an inter-metallic diffusion barrier that improves membrane stability for practical application. XPS analyses showed that the average surface compositions of the two membranes were respectively Pd84Cu16 and Pd46Cu54 (at.%). XRD analyses indicated that deposited Pd84Cu16 alloy film contained only α-fcc (face-centred cubic) phase structure whereas Pd46Cu54 alloy film contained a mixture of α-fcc and β-bcc phases. The 10 μm thick Pd46Cu54/ZrO2-PSS membrane exhibited an infinite separation factor for H2 over N2, with H2 permeance of 1.1 × 10−7 mol/m2 s Pa at 753 K. The activation energies for hydrogen permeation and hydrogen pressure exponents are respectively 14.5 kJ/mol and 0.6 for Pd84Cu16/ZrO2-PSS membrane and 15.4 kJ/mol and 1 for Pd46Cu54/ZrO2-PSS composite membrane. The different permeation properties for the two membranes are discussed in terms of different permeation mechanisms associated with membrane thickness, structure, surface composition and morphology.