Effects of Osmotic Flux on PdCu Alloy Membrane Structure

In this study, it was aimed to synthesize PdCu alloy membranes with firm, thin, and fcc phase structure (resistant to sulfur compounds), selectively permeable to hydrogen, using an electroless plating technique by creating an osmotic flux. First, coating studies were conducted without creating osmotic flux to determine the appropriate alloy formation temperature. Commercial porous borosilicate glass tubes were modified with alumina to form an interface that enhances the interaction between the coating and the support. The modified supports were cleaned and activated, then coated 3 times for 45 min in the Pd-based plating bath and then once for 15 min in the Cu-based plating bath. The coated supports were subjected to heat treatment at two different temperatures (550 and 650 °C) in a hydrogen environment for 8 h. Then, 650 °C, where the metals loaded on the surface were highly involved in the alloy structure and only the fcc phase was observed, was determined as the appropriate alloy temperature. Afterward, coating studies were conducted by creating osmotic flux with a 3 M sucrose solution, keeping the coating conditions and bath composition the same. From XRD analysis, fcc phase formation was observed in {111} {200} {220} planes in the membrane synthesized without osmotic flux, while alloy formation was detected in the {311} plane in addition to these planes in the membrane synthesized with osmotic flux. In this study, it has been shown that besides the temperature and time, the firmness of the metal layers formed before the heat treatment also affects the alloy formation in this plane. It was determined from SEM/EDS analyses that the membranes synthesized under the effect of osmotic flux were thinner, firmer, and homogeneous (⁓ 13.5 µm). Hydrogen transport parameters (T = 250 °C, ΔP = 101–304 kPa) were investigated in the synthesized membranes. In accordance with the literature, low hydrogen flux (0.04–0.09 mol/m² s) and high selectivity values (α_H2/N2:465–324) were determined in membranes synthesized with osmotic flux. Additionally, it was determined that this membrane remained stable in the hydrogen environment (T = 250 °C, ΔP = 203 kPa) for 96 h. The results of the study showed that conducting the electroless plating method with osmotic flux made positive contributions to the structure and hydrogen selectivity of the prepared alloy membranes.