Alloys at the Nanoscale; The Case of Nanoparticles Second Phase

技术摘要：金属纳米颗粒是有趣的纳米材料，因为它们可以投入大量的可能用途。一个例子是需要找到用于燃料电池的非铂基催化剂。很明显，在纳米尺寸水平上，合金化行为不能总是通过“本体”相图来预测，但是纳米颗粒系统的相图是不完整的，并且它们的确定构成了非常复杂的问题。目前的工作重点是建立可靠的纳米合金相图，包括Au-Pd，Au-Ag，Pt-Pd，Au-Co和Pd-Ir合金，所有这些都具有重要的潜在应用。这项工作的主要仪器是德克萨斯大学圣安东尼奥分校的新型STEM像差校正显微镜，分辨率为0.08纳米;它配备了最先进的EDS和EELS配件。STEM和TEM中的断层扫描方法将用于探索纳米颗粒的三维形状。这些颗粒将通过各种方法制备，这些方法已被证明对于生产具有可控尺寸、形状和结构分布的纳米颗粒是可靠的。预计对于给定的合金浓度，将出现导致核壳或Janus颗粒的条件的改进的理解。实验结果将与使用第一原理方法的稳定性和结构的理论计算进行比较。非技术概述：现代技术的最重要方面之一是在与化学工业相关的工业过程中使用贵金属，如铂，铑或钯。这些金属在自然界中是稀缺的，必须优化其使用。目前，如果美国所有的汽车都使用燃料电池，那么美国可能会消耗掉世界上所有的铂储量。因此需要新技术。在这项提案中，该团队参与了纳米粒子的使用。其目的是使用价值较低的金属如Cu、Au或Ag的核来尝试诱导活性更高的金属Pt、Pd或Rh的原子级薄的表面壳，以及探索两种金属的组合将暴露新性质的可能性。该项目将补充得克萨斯大学圣安东尼奥分校的PREM-NSF项目，也将有助于代表性不足群体的发展，因为几位博士参与该项目的学生是西班牙裔。在圣安东尼奥地区的初级学院，PI也有外展部分，以吸引西班牙裔学生参加2年制课程，然后参加完整的4年制课程。PI和Co-PI在招收少数民族学生方面具有丰富的经验。

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.