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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.

在该研究项目中，格鲁吉亚理工学院的Xia博士和威斯康星大学麦迪逊分校的Mavrikakis博士得到了大分子、超分子和纳米化学（MSN）计划的支持，以开发对聚合物电解质燃料电池的操作至关重要的氧还原反应（ORR）具有显著增强的质量活性的铂基催化剂。作为一种清洁能源技术，聚合物电解质燃料电池对于包括现场发电和用作运输车辆和电子设备的便携式电源的应用具有吸引力。然而，由于与沉积在阴极上用于减轻氧还原反应（ORR）的缓慢动力学的铂催化剂相关的高成本，大规模销售该技术一直是具有挑战性的。为了满足该技术大规模商业化的成本要求，需要将铂载量减少约四倍。Xia和Mavrikakis博士正在研究一种新的策略，该策略将化学合成和计算建模相结合，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只有几个原子层厚的超薄铂皮特别感兴趣。他们通过控制钯（Pd）模板上的小面类型（从而控制表面上原子的排列）、优化铂（Pt）皮的厚度以及最大化核中的钯原子与壳中的铂原子之间的电子耦合来开发具有增强活性的ORR催化剂。除了科学和技术的优点，这项工作有助于建立不同学科之间的联系，包括材料化学，催化，表面科学，计算化学，胶体科学和能源技术。它还对我们的社会产生影响，因为它开发了燃料电池和催化剂的新材料，在能源转换和环境保护中发挥作用。研究人员通过让妇女、少数民族和其他代表性不足的群体参与这个项目来促进高等教育的多样性。通过大幅减少催化装置中的Pt和Pd负载量，这项工作有助于社会实现对铂的可持续利用。铂是地壳中最稀有的贵金属之一。在聚合物电解质燃料电池的新型催化剂中，铂原子以共形壳的形式沉积在预先合成的钯纳米晶体的表面上，这些纳米晶体具有均匀的尺寸和良好的控制面。壳层厚度从一到五个原子层精确地调整。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，它们的每一个表面分别被一种类型的小面覆盖：{100}，{111}，{110}和高折射率的。这项研究涉及三种方法的独特组合：修改铂表面的电子结构通过控制钯核上的小平面来发展最活跃的表面结构;以及用钯（一种相对于铂便宜得多的金属）替换本体中的铂原子，以节省材料成本。这项研究的成果可能包括通过多学科和合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所涉及的非均质成核和生长机制;以及开发一类新型ORR催化剂，以目前的商业催化剂为基准时，其性能（活性和耐久性）与成本比有所改善。