Palladium and palladium alloy membranes for hydrogen separation and production: History, fabrication strategies, and current performance

Our aim is to survey the state-of-the-art in the development of palladium and palladium alloy membranes for hydrogen separations and hydrogen production. At the time this paper was written, several research groups have developed palladium and/or palladium alloy membranes with pure hydrogen permeances approaching 0.01 mol/m(2) s Pa-0.5. This includes our work to prepare Pd and Pd alloy composite membranes on stainless steel porous substrates with zirconia diffusion barriers. A 0.93 mu m thick pure Pd composite membrane on a Pall AccuSep (R) stainless steel substrate achieved a pure hydrogen flux of 1.3 mol/m(2) s at 400 degrees C and 1.38 bar differential pressure. The hydrogen flux values we have measured compare favorably to the U.S. DOE 2010 pure hydrogen flux performance target of 0.96 mol/m(2) s = 250 ft(3)(STP)/ft(2) h at conditions of 400 degrees C and a differential pressure of 20 psi or 1.38 bar. Pd alloy composite membranes containing Au and/or Ag show higher hydrogen flux than pure Pd membranes, as expected from the literature. At these same DOE test conditions of 400 degrees C and 1.38 bar, the pure hydrogen flux for a 2.3 mu m thick, Pd95Au5 composite membrane was 1.01 mol/m(2) s. Approximately the same pure hydrogen flux of 0.97 mol/m(2) s was measured for a thicker, 4.6 mu m, Pd80Ag20 composite membrane at 400 degrees C and 1.38 bar, consistent with the higher permeability of the Pd-Ag alloy compared to pure Pd and Pd-Au. Ideal H-2/N-2 separation factors of these composite membranes ranged from 337 to over 80,000. (C) 2009 Elsevier B.V. All rights reserved.