Atomic Layer-by-Layer Deposition of Pt on Pd Nanocrystals with Well-Controlled Facets

晶面可控的 Pd 纳米晶体上 Pt 原子层沉积

基本信息

批准号：
1505441
负责人：
Younan Xia
金额：
$ 30万
依托单位：
Georgia Tech Research Corporation
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2015
资助国家：
美国
起止时间：
2015-09-01 至 2018-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1505441&HistoricalAwards=false
关键词：
Atomic Layer Deposition Pt Pd

项目摘要

In this research project, Dr. Xia of the Georgia Institute of Technology and Dr. Mavrikakis of the University of Wisconsin-Madison are supported by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program to develop platinum-based catalysts with significantly enhanced mass activity toward the oxygen reduction reaction (ORR) critical to the operation of a polymer electrolyte fuel cell. As a clean-energy technology, polymer electrolyte fuel cells are attractive for applications that include on-site power generation and use as a portable power source for transportation vehicles and electronic devices. However, it has been challenging to market this technology on a large scale due to the high cost associated with the platinum catalysts deposited on the cathodes for mitigating the sluggish kinetics of the oxygen reduction reaction (ORR). A reduction of roughly four-fold in platinum loading is needed in order to meet the cost requirement for the large-scale commercialization of this technology. Drs. Xia and Mavrikakis are investigating a new strategy that integrates chemical synthesis and computational modeling for maximizing the mass specific activity of a platinum-based catalyst toward ORR. They are particularly interested in depositing platinum as ultrathin skins of only a few atomic layers thick on palladium nanocrystals. They develop ORR catalysts with enhanced activity by controlling the type of facet (and thus, the arrangement of atoms on the surface) on the palladium (Pd) templates, optimizing the thickness of the platinum (Pt) skin, and maximizing the electronic coupling between the palladium atoms in the core and the platinum atoms in the shell. In addition to the scientific and technological merits, this work helps forge links between different disciplines that include materials chemistry, catalysis, surface science, computational chemistry, colloidal science, and energy technology. It also impacts on our society because it develops novel materials for both fuel cells and catalysis that play a role in energy conversion and environmental protection. The researchers promote diversity in higher education by engaging women, minorities, and other underrepresented groups into this project. By substantially reducing Pt and Pd loadings in catalytic devices, this work helps society achieve a sustainable use for platinum, one of the rarest precious metals that exists in the Earth's crust.In the new catalysts for polymer electrolyte fuel cells, platinum atoms are deposited as conformal shells on the surfaces of palladium nanocrystals pre-synthesized with a uniform size and well-controlled facets. The shell thickness is precisely tuned from one to five atomic layers. Four types of palladium nanocrystals are investigated, including cubes, octahedra, rhombic dodecahedra, and concave cubes, with each one of their surfaces covered by a single type of facet: {100}, {111}, {110}, and high-index ones, respectively. This research involves a unique combination of three approaches: modification of the electronic structure of the platinum surface (and thus, the binding energies of oxygen-containing species) by coupling with the palladium core; development of the most active surface structure by controlling the facet on the palladium core; and replacement of the platinum atoms in the bulk with palladium, a much less expensive metal relative to platinum, to save the materials cost. The outcomes of this research may include enhancement of both graduate and undergraduate education through multidisciplinary and collaborative research; a deep understanding of the heterogeneous nucleation and growth mechanisms involved in the formation of metal nanocrystals; and the development of a novel class of ORR catalysts with an improved performance (activity and durability) to cost ratio when benchmarked against the current commercial catalyst.

在这个研究项目中，佐治亚理工学院的夏博士和威斯康星大学麦迪逊分校的马夫里卡基斯博士得到了高分子、超分子和纳米化学（MSN）计划的支持，开发质量活性显着增强的铂基催化剂氧还原反应（ORR）对于聚合物电解质燃料电池的运行至关重要。作为一种清洁能源技术，聚合物电解质燃料电池对于现场发电以及用作运输车辆和电子设备的便携式电源等应用具有吸引力。然而，由于沉积在阴极上用于缓解氧还原反应 (ORR) 缓慢动力学的铂催化剂成本高昂，大规模推向市场一直具有挑战性。为了满足该技术大规模商业化的成本要求，需要将铂负载量减少大约四倍。博士。 Xia 和 Mavrikakis 正在研究一种新策略，该策略将化学合成和计算模型结合起来，以最大限度地提高铂基催化剂对 ORR 的质量比活性。他们对在钯纳米晶体上沉积铂作为仅有几个原子层厚的超薄表皮特别感兴趣。他们通过控制钯 (Pd) 模板上的面类型（从而控制表面原子的排列）、优化铂 (Pt) 皮的厚度以及最大化之间的电子耦合来开发活性增强的 ORR 催化剂。核中的钯原子和壳中的铂原子。除了科学和技术优点外，这项工作还有助于在材料化学、催化、表面科学、计算化学、胶体科学和能源技术等不同学科之间建立联系。它还对我们的社会产生影响，因为它开发了用于燃料电池和催化的新型材料，在能源转换和环境保护方面发挥着作用。研究人员通过让女性、少数族裔和其他代表性不足的群体参与该项目来促进高等教育的多样性。通过大幅减少催化装置中铂和钯的负载量，这项工作有助于社会实现铂的可持续利用，铂是地壳中最稀有的贵金属之一。在用于聚合物电解质燃料电池的新型催化剂中，铂原子沉积为预合成的钯纳米晶体表面上的共形壳具有均匀的尺寸和良好控制的面。壳厚度从一到五个原子层精确调节。研究了四种类型的钯纳米晶体，包括立方体、八面体、菱形十二面体和凹立方体，它们的每个表面都被单一类型的面覆盖：{100}、{111}、{110}和高折射率分别是。这项研究涉及三种方法的独特组合：通过与钯核耦合来改变铂表面的电子结构（从而改变含氧物质的结合能）；通过控制钯核上的刻面来开发最活跃的表面结构；用钯（一种比铂便宜得多的金属）代替大量的铂原子，以节省材料成本。这项研究的成果可能包括通过多学科和协作研究加强研究生和本科生教育；深入了解金属纳米晶体形成中涉及的异质成核和生长机制；开发一类新型 ORR 催化剂，与当前商业催化剂相比，其性能（活性和耐久性）与成本比得到改善。