Optimized intermediate layer formation and electroless plating methods to obtain supported dense Pd surfaces

Dense metallic membranes, especially Pd and Pd alloys, have been intensely investigated to provide an alternative and economical way to obtain H₂ with ultrahigh purity. To overcome the high cost of Pd, composite membrane structures that comprise a thin layer of Pd are utilized. However, it is a challenge to obtain a thin, dense, and uniform Pd layer on the support materials. This study investigates the parametric analysis of γ-Al₂O₃ interlayer formation and the electroless Pd plating (Pd ELP) procedures on α-Al₂O₃ supports with the aim to achieve a thin, uniform Pd surface without annealing. Adjustments in PEG/PVA concentration, dipping time, and heat treatment enabled creating a thin γ-Al₂O₃ interlayer on α-Al₂O₃, minimizing pore size and density. Hydrazine concentration, heat treatment, and bath temperature were adjusted to optimize Pd ELP to achieve maximum yield from the plating bath and a dense, uniform surface without annealing. Pd/γ-Al₂O₃/α-Al₂O₃ structures were analyzed using scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis to observe the impact of varied parameters on surface structures. Optimized sample was compared to an annealed Pd/α-Al₂O₃ prepared in accordance with literature methods and a Pd/graphite/α-Al₂O₃ sample to validate the use of optimized ELP procedure and the γ-Al₂O₃ interlayer. Results show that a dense and uniform 13 μm Pd coating was achieved on a γ-Al₂O₃-coated α-Al₂O₃ support without annealing, using three fresh ELP baths. This was done using sequential hydrazine addition with a decreased concentration (1 M) into the ELP baths at 30 °C, and applying heat treatment at 120 °C between each fresh ELP bath.