CAREER: Room Temperature Electrochemical Synthesis of Ordered Intermetallic Nanomaterials

有序金属间化合物（OIC）是具有两种（或更多种）金属元素的周期性原子排列的金属合金。这些OIC在催化、电池和形状记忆合金等技术中发挥着重要作用。然而，它们的应用空间是有限的，因为这些材料只能在高温下制备，通常会侵蚀对重要材料参数的控制。要使低温合成OIC成为可能，需要精确了解原子如何在固体材料中移动。该学院早期职业奖（CAREER）将支持约翰霍普金斯大学Anthony Shoji Hall博士实验室的研究，以研究允许在低温下控制原子运动的途径，从而能够在室温和大气压下制备有序的金属间纳米材料。通过在低温下合成这些材料，这项工作将大大拓宽OIC的应用空间，因为它现在允许对重要材料参数进行更精细的控制。霍尔博士的实验室将通过在市中心巴尔的摩高中和大学开展外展活动，积极与更广泛的社区分享他们的科学激情和发现。第一项活动将利用一个既定的计划，干成就在巴尔的摩小学（SABES），以鼓励小学生追求干的程度。该项目还将创建一个新的计划，以鼓励URM高中学生攻读STEM学位，并提高URM（下）研究生在STEM职业中的保留率。尽管进行了数十年的深入研究，OIC纳米颗粒仍未能取代传统的纳米材料，原因是（1）缺乏低温合成方法，无法克服抑制原子有序的缓慢固态扩散速率，（2）无法调整成分和相位以优化所需的应用，以及（3）缺乏对这些问题的进展所需的基本理解。本CAREER提案的目的是通过去除较不贵重的组分（例如，将PdBi 2转化为Pd 3Bi，或将CuZn 4转化为Cu 5 Zn 8）。该项目的基本见解将使OIC纳米结构的合理发展与技术相关的应用，并提高我们对电催化条件下材料稳定性的理解。为了理解电化学脱合金介导的相变过程的起源，PI将研究以下目标：（1）阐明熔化温度对体扩散和晶格重组的作用。(2)开发控制去合金化OIC成分的合成方法。(3)通过原位光谱方法阐明脱合金。通过这种电化学介导的相转化过程制成的材料将作为锂金属电池的阳极进行评估，以证明合成方法的实用性。这一提议的更广泛影响将鼓励代表性不足的少数民族（URM）K-12学生和（下）研究生通过参与外展计划追求STEM事业。 由于代表性不足，URM学生无法获得STEM领域的相关榜样。为了解决这个问题，霍尔博士将使自己可用于非正式的“咖啡时间讨论”，作为一个导师和榜样的URM学生（高中年龄，本科生和研究生）在巴尔的摩地区。霍尔小组还将通过参加巴尔的摩小学STEM成就（SABES）计划，与K-12岁的URM学生合作开展基于探究的科学项目。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.