(288a) High-Throughput Characterization of the H2-D2 Exchange Activity of PdxCu1-X Alloys

Pd alloys have been widely studied as they are used as membrane materials to separate H₂ from mixed gas streams. In the mechanism of hydrogen permeation through the membrane the first step is dissociation of molecular H₂ on the alloy surface. In this study, we prepare Pd_xCu_1-x alloys and characterize the H₂ dissociation activities as a function of composition, x. The conventional approach in alloy research is to prepare and characterize a series of single composition samples, which is time consuming. To address this challenge, we have developed a high-throughput methodology that enables characterization of a range of alloy compositions in a single experiment.  The approach is based on use of Composition Spread Alloy Films (CSAFs), high-throughput libraries which include all possible alloy compositions of an alloy in the form of a thin film deposited on a substrate. In this work, Pd_xCu_1-x CSAFs were prepared by evaporative co-deposition of the components onto Mo substrates, followed by annealing at 700 K and H₂-D₂ exchange (H₂ + D₂ → 2HD) was used to probe the activity of film surface across composition and structure space.               

H₂-D₂ exchange experiments were performed using a multichannel microreactor array, at atmospheric pressure and over a temperature range from 60 to 320˚C. The array distributes 100 inlet-outlet pairs across the surface of the CSAF, enabling measurement of H₂ conversion at 100 discrete compositions on the CSAF in a single experiment. Binary Pd-Cu CSAFs, spanning the composition range 5-95% Pd, possess the features of the bulk phase diagram at the annealing temperature (700 K) and reveal increasing activity with increasing Pd content and increasing temperature. The maximum exchange activity was observed at ~70% Pd on the CSAF surface. The CSAF activity results are consistent with those obtained in a series of conventional experiments conducted over fixed beds of single composition bulk Pd-Cu alloys. Hence, this study shows that high-throughput methods provide reliable data and can be further used to characterize binary or higher order alloys.