High-Entropy Alloy Nanocrystals with Controlled Compositions and Surface Structures

成分和表面结构可控的高熵合金纳米晶

• 批准号: 2333595
• 负责人: Younan Xia
• 金额: $ 63.53万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-03-01 至 2027-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2333595&HistoricalAwards=false
• 关键词: Entropy; Alloy; Nanocrystals; Controlled; Compositions

NON-TECHNICAL SUMMARYThis grant supports research efforts to create a knowledge base for the rational and deterministic synthesis of high-entropy alloy (HEA, a complex solid comprised of five or more metals) nanocrystals with controlled surfaces in terms of both atomic composition and arrangement. Because of the diversity in composition, the surface of a HEA nanocrystal naturally presents an enormous number of atoms in distinct coordination environments to produce a near-continuum distribution of adsorption energies for the key intermediate of a reaction. As such, HEA nanocrystals offer a versatile platform for the rapid development of new catalytic materials. Despite some progress in recent years, it remains a grand challenge to control the composition and surface structure of HEA nanocrystals, making it impossible to quantitatively and accurately describe the structure-property relationship of HEA-based catalysts. During this project, a transformative technique is developed to achieve deterministic and even predictable synthesis of HEA nanocrystals with controlled compositions and surface structures. The as-obtained nanocrystals can directly serve as advanced catalytic materials to benefit U.S. economy and society. The multi-disciplinary and collaborative nature of this project offers a vehicle to enhance and enrich the education and training experiences of students while broadening the participation of underrepresented groups in cutting-edge research. In particular, the students learn firsthand how to discover and develop advanced catalytic materials twice as fast at a fraction of the cost. The results from this project are also adapted to enhance classroom teaching, including the development of demonstrations and experiments to better illustrate the key concepts of science and engineering. TECHNICAL SUMMARYThis research represents the first attempt to develop single-phase HEA nanocrystals with well-defined and controllable compositions and surface structures. Traditionally, colloidal synthesis of metal nanocrystals involves one-shot injection of the metal precursor. When directly applied to a bi- or multi-metallic system, such a protocol is subject to failures because different precursors have distinct reduction kinetics and their instantaneous concentrations in the reaction solution would decay differently with reaction time. Parting from the traditional method, the investigators co-titrate the solutions of different precursors dropwise into a reaction solution so that the instantaneous concentration of each precursor is kept in a predefined steady state throughout the synthesis. As a result, metal atoms are produced from the different precursors at stable, pre-specified rates for the generation of HEA nanocrystals with a uniform composition, with the atomic ratios determined by the reduction rates of their precursors in the steady states. When conformally deposited on preformed seeds with different shapes as overlayers of a few atomic layers in thickness, HEA nanocrystals with well-defined facets are obtained. The seeds can be selectively etched away to release the HEA overlayers as ultrathin nanoplates. At a thickness of three atomic layers, the nanoplates are perfect for resolving the composition and surface structure by electron microscopy and spectroscopy. In parallel, the HEA nanocrystals are tested for catalytic reactions, with a focus on the identification of a catalyst optimal in activity and durability toward oxygen reduction and bond-selective hydrogenation. The synthetic method can also be extended to accelerate the rational development of other types of nanomaterials with complex compositions for a range of applications, including those related to chemical production, petroleum industry, national security, and public health.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.

非技术摘要这项资助支持研究工作，以创建一个知识库，用于合理和确定性地合成高熵合金（HEA，一种由五种或更多金属组成的复杂固体）纳米晶体，其表面在原子组成和排列方面均受到控制。由于成分的多样性，HEA 纳米晶体的表面天然存在大量处于不同配位环境中的原子，从而为反应的关键中间体产生近连续的吸附能分布。因此，HEA 纳米晶体为新型催化材料的快速开发提供了一个多功能平台。尽管近年来取得了一些进展，但控制 HEA 纳米晶体的组成和表面结构仍然是一个巨大的挑战，因此无法定量、准确地描述 HEA 基催化剂的结构-性能关系。在该项目中，开发了一种变革性技术，以实现具有受控成分和表面结构的 HEA 纳米晶体的确定性甚至可预测的合成。所获得的纳米晶可以直接作为先进催化材料造福美国经济和社会。该项目的多学科和协作性质为增强和丰富学生的教育和培训经验提供了一种工具，同时扩大了代表性不足的群体对前沿研究的参与。特别是，学生们可以直接学习如何以两倍的速度以极低的成本发现和开发先进的催化材料。该项目的成果也适用于加强课堂教学，包括开发演示和实验，以更好地说明科学和工程的关键概念。技术摘要本研究首次尝试开发具有明确且可控的成分和表面结构的单相 HEA 纳米晶体。传统上，金属纳米晶体的胶体合成涉及金属前体的一次性注入。当直接应用于双金属或多金属系统时，这种方案可能会失败，因为不同的前体具有不同的还原动力学，并且它们在反应溶液中的瞬时浓度会随着反应时间的不同而衰减。与传统方法不同，研究人员将不同前体的溶液逐滴共同滴定到反应溶液中，以便在整个合成过程中每种前体的瞬时浓度保持在预定的稳态。结果，金属原子以稳定的、预先指定的速率从不同的前体中产生，以生成具有均匀成分的HEA纳米晶体，原子比由其前体在稳态下的还原率决定。当共形沉积在不同形状的预成型种子上作为几个厚度的原子层的覆盖层时，可以获得具有明确刻面的 HEA 纳米晶体。可以选择性地蚀刻掉种子，以将 HEA 覆盖层释放为超薄纳米板。纳米板的厚度为三个原子层，非常适合通过电子显微镜和光谱法解析成分和表面结构。同时，对 HEA 纳米晶体进行催化反应测试，重点是确定对氧还原和键选择性氢化具有最佳活性和耐久性的催化剂。该合成方法还可以扩展到加速其他类型的具有复杂成分的纳米材料的合理开发，其应用范围广泛，包括与化学生产、石油工业、国家安全和公共卫生相关的应用。该奖项反映了 NSF 的法定使命和通过使用基金会的智力优点和更广泛的影响审查标准进行评估，该项目被认为值得支持。