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 Pd ₄₆Cu₅₄ (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 Pd ₈₄Cu₁₆/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.