Development of Pd Alloy Membranes for Ultrapure Hydrogen Production

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Multicomponent alloy materials are used in a variety of applications in which surface properties are critical. For Pd-based alloys used as dense metal membranes in hydrogen purification processes, critical surface properties include the ability of the alloy surface to dissociate H2 and its ability to resist contamination. A fundamental alloy characteristic that can influence both of these properties is surface segregation, the propensity of the alloy's surface composition to differ from its bulk composition. The proposed effort will develop and apply a novel, high-throughput methodology for fundamental study of these surface properties in Pd100-x-yAgxRuy and Pd100-x-yAgxCuy alloys. This approach will enable measurement of segregation, H2 dissociation kinetics, and sulfur poisoning across continuous regions of alloy composition space, providing an unprecedented and comprehensive understanding of how these surface properties depend on composition. One of the challenges inherent in the study of multicomponent materials is that of understanding their properties over a wide range of composition space without the need to prepare and characterize a prohibitively large set of discrete, fixed-composition samples. For efficient study of alloy surfaces, the PIs have recently developed two unique tools that will serve as the basis for the proposed investigation. The first is a deposition source for preparation of Composition Spread Alloy Films (CSAFs), such as Pd100-x-yAgxRuy, with lateral gradients in composition across their surfaces, thus exposing all possible alloy compositions on a single compact (~1 cm2) substrate. The second tool is a 10x10 multichannel microreactor for spatially resolved measurement of reaction kinetics on CSAF surfaces. In the proposed research, these tools will be combined with spatially resolved surface analysis techniques to deliver a fundamental understanding of the composition dependence of a number of alloy surface properties that are critical to the performance of dense metal hydrogen separation membranes. The tools and methods for preparation and characterization of CSAFs that are developed and refined during the proposed research program will be applied broadly to the study of alloy properties far beyond those relevant to hydrogen purification membranes. Highthroughput study of alloy hardness, corrosion resistance, catalytic activity for fuels conversion reactions, etc., will generate comprehensive data sets across all possible compositions for a nearlimitless number of binary, ternary and even higher order alloys. The proposed work will train students in the application of high-throughput approaches to a wide variety of problems in alloy materials science. Collaborations with Universidad Nacional del Litoral in Santa Fe, Argentina and the Department of Energy's National Energy Technology Laboratory will give students opportunities to work with world-class scientists outside Carnegie Mellon; we plan to pursue separate funding that would support student travel to work in Argentina. Students from Argentina will also benefit from their exposure to this research and their interactions with Carnegie Mellon researchers. The results of the proposed work will be disseminated to the scientific community through publications and presentations at national meetings. Beyond the research impact of the proposed work, the PIs are very active in the research community; they serve several professional organizations in various capacities, including organization of research symposia on topics related to high-throughput catalysis and surface science. They are also active in service to professional student organizations.