Nanometric Effects at Ultra-Small Crystallite Size: Investigation of Low-Temperature Protonic Conductivity in Dense Functional Oxide Ceramics

超小微晶尺寸的纳米效应：致密功能氧化物陶瓷中低温质子电导率的研究

• 批准号: 0709740
• 负责人: Zuhair Munir
• 金额: --
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-15 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0709740&HistoricalAwards=false
• 关键词: Nanometric; Effects; Ultra; Small; Crystallite

This research project is a collaborative effort between the Department of Chemical Engineering and Materials Science (Professors Z. A. Munir and S. Kim) at the University of California, Davis and the Institute of Physical Chemistry (Professor M. Martin) at RWTH Aachen University, Germany. The goal of this research is to provide an understanding of the heretofore-unobserved proton and oxygen transport processes in dense, nanocrystalline oxides, as an example of the nanoscale effect in functional oxides. The investigators' ability to prepare oxides with ultra-small grain size (approaching 10 nm) has opened a window of investigation on this and on related nanometric effects. The aim is to prepare and investigate such materials in dense, bulk form with even smaller grain size ( 10 nm). Observation of the occurrence of low-temperature protonic conductivity in unhydrated yttria-stabilized zirconia and doped ceria, typical predominant oxygen ion conductors, opens a new door on the fundamental issue of a unique behavior of nanostructured electroceramics. Heretofore such a behavior has not been observed since prior attempts to prepare such materials in bulk form had not been successful. The researchers' success was made possible by their unique ability (through a novel pressure assisted field activated sintering method) to prepare highly dense ( 98%), bulk, nanometric oxides with a grain size of 20 nm. The fundamental questions that arise from their observations include: what is the nature of this protonic conduction? What is the mechanism associated with protonic mobility? Since this phenomenon is only observed in materials with ultra-small grain size, how do grain boundaries play a role in mass and charge transport? In view of observation on thin films, are the role and nature of grain boundaries different when the grains are very small? What, if any, do dopant-generated point defects contribute to the process? The answers to these and related fundamental questions should provide a significant intellectual contribution to our understanding of the nanoscale effect in these functional oxides and stimulate new research in this important area. The use of stable oxides with mechanical integrity as protonic conductors at low temperatures (even in water at room temperature) has an immense impact on application considerations for protonic conductors. Protonic conductors have an extensive field of application, including their use as hydrogen separators (when used as mixed conductors), or to produce power (when used in fuel cells). They can also be used in electrolysis for hydrogen production, and for reactions to hydrogenate and dehydrogenate organic compounds. Current solid oxide fuel cells require high temperatures (800 - 1000C), a condition that presents material degradation problems, as well as other technological complications and economic obstacles. The economic considerations alone make broad commercialization prohibitive. An effective way to reduce the cost is to reduce the operating temperature without scarifying fast electrode kinetics and high ionic conductivity of the electrolyte, which our results has demonstrated its feasibility. It is to be emphasized that the observed low-temperature protonic conductivity occurs at room temperature without the need to apply a catalyst. The results show that with optimization, viable power generation using water concentration cells at room temperature is a possible goal. An important aspect of the research is the participation and exchanges of graduate and undergraduate students and postdoctoral fellows. In addition to faculty exchange visits, an exchange program for students and postdoctoral fellows is planned. Each graduate student (both from Germany and the US) will go through the entire process from synthesis and consolidation and structural and electrical characterization (at UC Davis) to SIMS determinations (at RWTH Aachen University).

本研究计画是化学工程与材料科学系（Z。A. Munir和S. Kim）在加州大学戴维斯分校和物理化学研究所（M.马丁）在亚琛工业大学，德国。这项研究的目的是提供一个迄今未观察到的质子和氧的传输过程中的致密，纳米晶氧化物的理解，作为一个例子的功能氧化物的纳米级效应。研究人员制备具有超小晶粒尺寸（接近10 nm）的氧化物的能力为研究这一点和相关的纳米效应打开了一扇窗。目的是制备和研究这种材料的致密，散装形式，甚至更小的晶粒尺寸（10纳米）。在未水合氧化钇稳定的氧化锆和掺杂氧化铈，典型的主要氧离子导体的低温质子导电性的发生的观察，打开了一个新的门的纳米结构的电瓷的独特行为的基本问题。 然而，由于先前以散装形式制备这种材料的尝试没有成功，因此没有观察到这种行为。研究人员的成功是由于他们独特的能力（通过一种新的压力辅助场活化烧结方法），以制备高密度（98%），散装，纳米氧化物的晶粒尺寸为20纳米。从他们的观察中产生的基本问题包括：这种质子传导的性质是什么？与质子迁移率有关的机制是什么？由于这种现象只在超小晶粒尺寸的材料中观察到，那么晶界在质量和电荷传输中是如何发挥作用的呢？从对薄膜的观察来看，当晶粒很小时，晶界的作用和性质是否不同？掺杂剂产生的点缺陷对工艺有什么影响？ 这些和相关的基本问题的答案应该提供一个显着的智力贡献，我们的理解在这些功能氧化物的纳米效应，并刺激在这一重要领域的新的研究。使用具有机械完整性的稳定氧化物作为质子导体在低温下（甚至在室温下的水中）对质子导体的应用考虑具有巨大的影响。质子导体具有广泛的应用领域，包括它们用作氢分离器（当用作混合导体时）或产生电力（当用于燃料电池时）。它们也可以用于电解制氢，以及用于分解和分解有机化合物的反应。目前的固体氧化物燃料电池需要高温（800 - 1000 ℃），这是一种存在材料降解问题以及其他技术复杂性和经济障碍的条件。仅仅是经济上的考虑就使广泛的商业化成为不可能。降低成本的一个有效途径是在不牺牲快速电极动力学和高离子电导率的电解质的情况下降低操作温度，我们的研究结果已经证明了它的可行性。需要强调的是，所观察到的低温质子导电性发生在室温下，而不需要施加催化剂。结果表明，通过优化，在室温下使用水浓缩电池进行可行的发电是一个可能的目标。研究的一个重要方面是研究生和本科生以及博士后研究员的参与和交流。除了教师交流访问外，还计划为学生和博士后研究员提供交流计划。每个研究生（来自德国和美国）将经历从合成和巩固，结构和电气表征（在加州大学戴维斯分校）到西姆斯测定（在RWTH亚琛大学）的整个过程。