ABSTRACT

Non-Technical Summary:
Ordered intermetallic compounds (OICs) are metallic alloys with a periodic atomic arrangement of two (or more) metal elements. These OICs play an important role in technologies such as catalysis, batteries, and shape-memory alloys. Their application space is limited, however, because these materials can only be prepared at high temperatures, often eroding control over important material parameters. Making the low-temperature synthesis of OICs possible requires a precise understanding of how atoms move within solid materials. This Faculty Early Career Award (CAREER) will support research in the laboratory of Dr. Anthony Shoji Hall at the Johns Hopkins University to examine pathways that allow for the control of atom movement at low temperatures and thereby enable the preparation of ordered intermetallic nanomaterials at room temperature and atmospheric pressure. By enabling the synthesis of these materials at low temperatures, this work will substantially broaden the application space of OICs because it now allows for more fine control over important materials parameters. Dr. Hall?s laboratory will actively share their scientific passion and discoveries with the broader community by engaging in outreach at inner-city Baltimore high schools and universities. The first activity will leverage an established program, STEM achievement in Baltimore elementary schools (SABES), to encourage elementary students to pursue a degree in STEM. This project will also create a new program to encourage URM high school students to pursue degrees in STEM and to improve the retainment of URM (under)graduate students in STEM careers.

Technical Summary:
Despite decades of intense research, OIC nanoparticles have failed to replace conventional nanomaterials due to (1) lack of low-temperature synthetic methods that can overcome slow solid-state diffusion rates which inhibits atomic ordering, (2) inability to tune composition and phase to optimize the desired application, and (3) lack of fundamental understanding needed for progress on these issues. The purpose of this CAREER proposal is to examine the phase transformations of low melting point alloys to higher melting point OICs richer in the nobler and more active metal at ambient temperature and pressure by removal of the less noble component (e.g., transforming PdBi2 to Pd3Bi, or CuZn4 to Cu5Zn8) via a process known as dealloying. Fundamental insights from this project will enable the rational development of OIC nanostructures for applications of technological relevance and improve our understanding of material stability under electrocatalytic conditions. To understand the origin of the electrochemical dealloying-mediated phase conversion process, the PI will investigate the following objectives: (1) Elucidate the role of melting temperature on bulk diffusion and lattice reorganization. (2) Develop synthesis methods for controlled compositions of de-alloyed OICs. (3) Elucidate dealloying via in-situ spectroscopic methods. Materials made by this electrochemically mediated phase conversion process will be evaluated as anodes for Li-metal batteries to demonstrate the utility of the synthetic method. The broader impacts of this proposal will encourage underrepresented minority (URM) K-12 students and (under)graduate students to pursue careers in STEM through engagement in outreach programs. URM students lack access to relatable role models in STEM fields because of underrepresentation. To address this issue, Dr. Hall will make himself available for informal ?coffee hour discussions? to serve as a mentor and role model for URM students (high school-aged, undergraduate, and graduate students) in the Baltimore area. The Hall group will also work with K-12 aged URM students on inquiry-based scientific projects by participating in the STEM Achievement in Baltimore Elementary Schools (SABES) program.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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