Hydrogen permeability and membrane durability of novel pd/γ-alumina graded membrane when a sweep gas is used

In this study, Pd/γ-alumina graded membranes were fabricated by an electroless plating method on nanoporous γ-alumina formed by anodic oxidation of an etched aluminum support, and the H₂ permeability of the membranes was determined. The Pd/γ-alumina graded membrane on the etched aluminum support was prepared by carrying out electroless plating for 30 min, and for 60 min. In the first case of electroless plating for 30 min, Pd/γ-alumina graded membrane with a thickness of 2.5 μm, H₂ flux of 0.28 mol m^-2 s^-1, and H₂/N₂ permselectivity of 817 were obtained. In the second case of electroless plating for 60 min, Pd/γ-alumina graded membrane with a thickenss of 4.5 μm, H₂ flux of 0.17 mol m^-2 s^-1, H₂/N₂ permselectivity of 5259 were obtained. In durability tests, it was observed that the H₂ flux increased with time in the initial stage and then become approximately constant after 70 h. The graded membrane exhibited high durability. The membrane formed by 60 min of electroless plating was heated at 773 K for 12 h in a furnace (preheated Pd/γ-alumina graded membrane). The H₂ flux of the preheated graded membrane remined approximately constant during the durability test. This result implies that the Pd/γ-alumina graded membrane for the optimum H₂ permeation was not obtained by heating because the Pd crystals formed by electroless plating, and recrystallized to form larger grains; this happened because of heating, hybridization of γalumina and Pd, and influence of annealing. Finally, we successfully fabricated novel Pd/γ-alumina graded membranes that exhibited high H₂/N₂ permselectivity, H₂ permeability, and durability.