Predicting, Fabricating, and Permeability Testing of Free-Standing Ternary Palladium−Copper−Gold Membranes for Hydrogen Separation

Abstract

For hydrogen from coal gasification to be used economically, novel separation processes that produce highpurity H 2 must be developed. While binary palladium based alloys have shown promising pure hydrogen flux values, the search for optimal binary or ternary alloys is an involved and costly process due to the immense number of alloy variations that can be prepared and tested. In this paper an approach to identify, fabricate, and experimentally verify the hydrogen permeation performance of PdCu and PdAu binary alloys and ternary alloys of PdCuAu at various copper and gold concentrations to produce robust, poison-tolerant, hydrogen selective free-standing membranes is reported. This approach utilizes three primary tasks of (1) materials modeling and composition selection, (2) fabrication of high-performance binary and ternary alloy membranes, and (3) membrane testing and evaluation that are all operating independently and concurrently. For the binary Pd-Cu system, using a pure Pd membrane as the reference, both the theoretically predicted and experimentally measured additions of copper lowered the hydrogen permeability. For the binary Pd-Au system, the addition of gold slightly lowered permeability in the theoretical model but in the experimental testing was enhanced. For the ternary system, both experimental and theoretical permeabilities were depressed, with Cu exhibiting a larger influence on reducing the permeability.

Surface composition of PdCuAu ternary alloys: a combined LEIS and XPS study

“…Note that our results are consistent with the previous reports. We observed that the introduction of gold to the PdCu binary improves hydrogen permeation, in agreement with the data previously reported for magnetron‐sputtered samples . Peters et al .…”

“…Bredesen and coworkers reported a complete fcc alloy formation with no evidence of the bcc crystalline phase for Pd 71.5 Cu 27 Au 1.5 and Pd 72.1 Cu 24.7 Au 3.2 alloys synthesized by magnetron sputtering. On the other hand, Coulter et al . modeled and fabricated by magnetron sputtering several PdCuAu membranes with different compositions, obtaining a fcc structure in all cases.…”

First-principles study of hydrogen permeation in palladium-gold alloys

“…3,4 Alloying inevitably influences other key parameters such as the permeability of H. Unexpectedly, however, at low alloying levels Pd membranes show values of the H permeability higher than in pure Pd. [5][6][7][8][9] The origin of this behavior is still elusive to date. This firstprinciples study addresses this issue in the case of PdAu alloys.…”

“…Experimental reports on the enhanced permeability of H in PdAu alloys date back to 1869. 5 Today, this issue is still matter of both experimental [7][8][9] and theoretical [10][11][12][13] scrutiny. Experiments show that at very low Au contents the permeability of the alloy is larger than that of Pd.…”

Pd-Alloy membranes for hydrogen separation

“…In a series of PdCuAu ternaries with Pd between 53% and 87% (at) and Au from 3% to 8%, Coulter observed that substitution of Au for Cu increases the permeability of the parent PdCu alloy [50]. Substitution of Ag for Cu in PdCu also improves permeability: Tarditi reported that a Pd 68 Cu 25 Ag 7 alloy is 3.9 times as permeable as Pd 67 Cu 33 [51].…”