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

Abstract

Dense metallic membranes, especially Pd and Pd alloys, have been intensely investigated to provide an alternative and economical way to obtain H 2 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-Al 2 O 3 interlayer formation and the electroless Pd plating (Pd ELP) procedures on α-Al 2 O 3 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-Al 2 O 3 interlayer on α-Al 2 O 3 , 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-Al 2 O 3 /α-Al 2 O 3 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-Al 2 O 3 prepared in accordance with literature methods and a Pd/graphite/α-Al 2 O 3 sample to validate the use of optimized ELP procedure and the γ-Al 2 O 3 interlayer. Results show that a dense and uniform 13 μm Pd coating was achieved on a γ-Al 2 O 3 -coated α-Al 2 O 3 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.