Alloys at the Nanoscale; The Case of Nanoparticles Second Phase

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TECHNICAL SUMMARY: Nanoparticles of metals are interesting nanomaterials because of the large number of possible uses to which they can be put. An example is the need to find non-platinum-based catalysts for fuel cells. It is clear that at the nano-size level, alloying behavior cannot always be predicted by "bulk" phase diagrams, but phase diagrams of nanoparticle systems are not complete and their determination poses a very complex problem. A focus of the present work is to establish reliable phase diagrams of nanoparticle alloys, including Au-Pd, Au-Ag, Pt-Pd, Au-Co and Pd-Ir alloys, all of which have important potential applications. Major instrumentation for this work is the new STEM aberration-corrected microscope with a resolution of 0.08 nm at the University of Texas at San Antonio; it is equipped with state-of-the-art EDS and EELS accessories. Tomography methods in the STEM and TEM will be used to explore the shapes of the nanoparticles in 3 dimensions. The particles will be prepared by a variety of methods, which have proved to be reliable for the production of nanoparticles with controlled size, shape and structure distribution. It is expected that improved understanding will emerge of the conditions leading to core shell or Janus particles for a given alloy concentration. Experimental results will be compared with theoretical calculations of stability and structure using a first principles approach.NON-TECHNICAL SUMMARY: One of the most important aspects of modern technology is the use of precious metals such as platinum, rhodium or palladium in industrial process related to the chemical industry. These metals are scarce in nature and their use has to be optimized. Currently, if all of the cars in the United States used fuel cells, the nation would likely consume all of the Pt reserves in the world. New technologies are thus required. In this proposal the team is involved in the use of bimetallic nanoparticles. The aim is to use a core of a less valuable metal such as Cu, Au, or Ag to try to induce an atomically thin surface shell of the more active metal Pt, Pd or Rh, as well as to explore the possibility that the combination of the two metals will expose new properties. This project will complement a PREM-NSF program at the University of Texas at San Antonio and will also contribute to the advancement of underrepresented groups, since several of the Ph.D. students involved in the project are Hispanics. The PIs also have outreach components in the Junior Colleges of the San Antonio Area to induce Hispanic students to enroll in the 2-year program and then to a full 4-year program. The PI and Co-PI have considerable experience in recruiting minority students.