High flux palladium–copper composite membranes for hydrogen separations

Composite Pd alloy membranes have been investigated as a means of reducing the membrane cost and improving H2 flux. Recently, we have been able to dramatically reduce the thickness of our Pd alloy membranes to approximately one micron. This is significant because at this thickness, it is the cost of the porous support that controls the materials cost of the composite Pd alloy membrane, not the palladium inventory. We have prepared a 1.3-micronthick Pd95Cu5 (composition given in mass %) alloy film, coated on a Pall Corporation Membralox® T1-70 tubular ceramic substrate, which nearly meets the DOE pure hydrogen flux target of 200 scfh/ft2 at 400°C and 20 psi hydrogen partial pressure.

Fig. 4. Pd/Cu phase diagram [40]. Pd/Cu alloy membranes were deposited on ceramic supports by electroless plating. Membranes as thin as 1.3 µm were fabricated and tested. The Pd plating bath recipe was modified by removing EDTA in an effort to reduce or elimi- nate carbon contamination in the resulting Pd membranes. Membranes fabricated utilizing the modified plating recipe exhibited higher permeabilities than those prepared with plating baths containing EDTA. Hydrogen flux values of a Pd95Cu5 membrane at 365°C and 20 psi hydrogen partial pressure exceeded 190 scfh/ft2, which nearly met the US DOE target of 200 scfh/ft2 at 400°C. These results indicate that the DOE flux target can be met or even exceeded by optimizing the alloy compostition of the membrane.