(785f) High Throughput Study of Ternary Pd-Alloys for Applications in Hydrogen Separation

Separation of hydrogen from mixed gas streams is an important unit operation in generation of carbon-neutral fuels and electricity from fossil- and bio-derived feedstocks.  Pd-based membranes have received significant attention for the separation application in advanced coal gasification processes because of their near-perfect selectivity for hydrogen. In practice, pure Pd suffers from several limitations, including high cost, poor mechanical strength, and deactivation by minor components, most notably H₂S. H₂S can compromise membrane performance by reacting with Pd to form a low-permeability Pd₄S scale on the membrane surface.  Pd has been alloyed with minor components to improve structural properties, improve permeability and impart resistance to H₂S. To achieve both high permeability and H₂S tolerance, we are applying high-throughput methodologies to development of Pd_xCu_yAu_1-x-y ternary alloys across continuous composition space (x, y= 0 to 1).

Using e-beam PVD sources and a masking system of our own design, we deposited Pd_xCu_yAu_1-x-y composition spread alloy films (CSAFs), thin (~100 nm) alloy films spanning broad, continuous composition space (x, y = 0 to 1), onto compact (14 x 14 mm) substrates. Structural characterization of an annealed (530 °C) CSAF, by electron backscatter techniques, reveals that addition of more than ~ 20 atom % Au prevents formation of the BCC form that displays high H-atom permeability in the PdCu binary.  H₂-D₂ exchange activity measurements, performed using a unique multichannel reactor array of our own design, show that the alloy is most active for hydrogen dissociation at high Pd contents. Finally, surface composition characterization of an annealed CSAF that had been exposed to 1000 ppm H₂S in H₂ at 350 °C shows that sulfur uptake by the alloy is lowest at compositions in the vicinity of Pd_0.40Cu_0.20Au_0.40, suggesting that the CuAu combination is more effective than either Au alone or Cu alone for improving Pd’s resistance to sulfur corrosion.

Results of permeability tests of prototype membranes made by sequential electroless deposition methods, with compositions suggested by the high throughput studies, will also be presented.