Integrated ceramic minichannel and microchannel membrane networks comprised of cordierite monoliths packaged with appropriate fluid distribution are being developed for hydrogen extraction from hydrocarbons. The final membrane design is envisioned as a catalytic steam reforming layer; over top a hydrogen-permselective palladium layer. By combining these technologies it is expected to produce ultra pure hydrogen in a single integrated device for portable power systems application¹. In this talk, we present progress to-date in coating thin permselective palladium films within the cordierite minichannel network for hydrogen purification.

In this study, palladium films have been deposited by electroless plating on top of an alumina supporting layer, itself deposited within a cordierite matrix. The alumina supporting layer was coated inside the cordierite channels by wash-coating method to achieve a smooth, uniform coat.  This was accomplished in two steps, first laying down a micro-sized layer of γ-alumina to achieve a low-stress deposition surface, followed by deposition of a nano-sized γ-alumina layer to produce a smooth, crack-free, and pinhole-free alumina layer that is ideal for plating Palladium. Two electroless plating methods were compared for depositing thin Palladium films on the resulting substrate. Each palladium film was tested for permeability and permselectivity by flowing hydrogen / helium mixtures through the channels at 350°C.    

In this talk we will present details on the coating methods used to prepare the cordierite substrate, plating techniques for realizing permselective membranes, and packaging strategies to ensure stable, leak-free operation. With this there will be a general discussion of how these different variables factor into the selectivity and permeability of the resulting membrane.  SEM imaging and EDS analysis were used to examine the thin film morphology. Leak testing and selectivity testing were used to examine the overall performance of the palladium films.  To-date, films have been developed that achieve a hydrogen permeation rate of 0.004-0.017moles/m²s, and hydrogen-to-helium selectivities of  40-100.

¹ B.A. Wilhite, S.E. Weiss, J.Y. Ying, M.A. Schmidt and K.F. Jensen, "Demonstration of 23wt% Ag-Pd Micromembrane Employing 8:1 LaNi_0.95Co_0.05O₃/Al₂O₃ Catalyst for High-Purity Hydrogen Generation," Advanced Materials, 18, 1701 (2006).