Nanostructured Palladium-based Alloy Catalysts for Fuel Cells

化石燃料的迅速枯竭和日益增长的环境担忧，在全球范围内创造了对替代清洁能源技术的巨大需求。能源是21世纪人类面临的最大挑战。燃料电池为解决从便携式到汽车再到固定动力的各种能源需求提供了巨大的希望，减少了我们对石油的全球依赖，并促进了未来的能源安全、繁荣和更清洁的环境。然而，燃料电池技术面临着与耐用性、性能和成本相关的众多材料挑战，阻碍了商业化前景。从2004年国家研究委员会/国家工程院的报告和美国物理学会的报告中可以看出，对燃料电池材料的化学和物理过程有深刻的基本了解，对于实现重大突破至关重要，这些突破将导致以负担得起的成本提高燃料电池的性能。例如，目前使用的铂催化剂成本高，资源有限，这给燃料电池的商业化前景带来了严重的问题。这项提议通过探索新的钯基合金催化剂解决了这一关键问题；钯的成本是铂成本的五分之一。设计了一种用于氧还原反应(ORR)的纳米结构钯基合金催化剂，其原理是将良好的氧键断裂金属(如Co)与良好的氧还原金属(如Pd)配对，以形成吸附的氧，从而有效地将吸附的氧原子还原为氧离子。潜在的催化剂组成通过循环伏安(CV)用玻碳微电极筛选来确定。采用反相微乳液法和多元醇还原法制备了由钯和其他金属如钛、钒、铬、铁、钴、镍、铜、钼、钨、Ru、Au和铂组成的多金属二元和三元合金组合物，然后在中等温度下进行热处理，以获得高度的合金化和均匀性、小而均匀的粒度分布、高的催化活性和良好的化学稳定性。用各种物理技术对合金催化剂进行了表征，包括衍射、显微镜、光谱和电化学测量(循环伏安法、线性极化法和旋转圆盘电极法)。对单电池质子交换膜燃料电池和直接甲醇燃料电池中氧还原反应(ORR)和甲醇氧化反应(MOR)的催化活性进行了评价。在研究结果的基础上，对催化机理有了基本的了解。智力上的优点是：(I)对控制燃料电池中氧还原反应和甲醇氧化反应的纳米结构钯基合金催化剂的电催化活性的因素有基本的科学理解，以及(Ii)利用这些知识设计和开发新的更便宜、更高效的燃料电池用钯基催化剂。在指导思想的指导下，采用可控的低温合成方法来制备钯基合金催化剂，以保持较小的颗粒尺寸和最大限度的催化活性，通过循环伏安法进行筛选，并通过各种物理、化学和电化学技术进行表征，以确定相关的催化机理。拟议的研究活动将加强我们对电催化剂的结构-性能-性能关系和燃料电池技术的商业化前景的基本了解。广泛的影响：拟议的研究为学生提供了一个独特的、全国重要的能源转换材料领域的更广泛的跨学科培训，包括材料化学和电化学科学与工程。在这一领域实现强大的科学基础有助于设计和开发便携式、汽车和固定应用的新材料，这将产生深远的社会影响。拟议的活动还旨在招募和培训少数族裔和女性学生，并对K-12学生和普通公众进行清洁能源技术和材料方面的教育。

The rapid depletion of fossil fuels and growing environmental concerns have created enormous worldwide demand for alternative, clean energy technologies. Energy is the single greatest challenge facing humankind in the 21st century. Fuel cells offer tremendous promise for solving a variety of energy needs ranging from portable to automobile to stationary power, reducing our global dependence on oil and fostering future energy security, prosperity, and a cleaner environment. However, fuel cell technologies are confronted with numerous materials challenges associated with durability, performance, and cost, impeding the commercialization prospects. As evident from the 2004 National Research Council/National Academy of Engineering report and the American Physical Society report, a profound fundamental understanding of the chemical and physical processes in fuel cell materials is vital for enabling significant breakthroughs that will lead to enhanced fuel cell performance at an affordable cost. For example, the high cost and limited abundance of the currently used platinum catalysts pose serious problems for the commercialization prospects of fuel cells. This proposal addresses this critical issue by exploring new palladium-based alloy catalysts; the cost of palladium is one-fifth of the cost of platinum. Nanostructured palladium-based alloy catalysts for oxygen reduction reaction (ORR) are designed based on a guiding principle involving the pairing of a good oxygen-bond cleaving metal such as Co for first splitting the O-O bond to form adsorbed oxygen with a good oxygen-reduction metal such as Pd for efficiently reducing the adsorbed oxygen atoms to oxide ions. Potential catalyst compositions are identified by a cyclic voltammetric (CV) screening with glassy carbon microelectrodes. Multi-metallic binary and ternary alloy compositions consisting of palladium and other metals like Ti, V, Cr, Fe, Co, Ni, Cu, Mo, W, Ru, Au, and Pt are synthesized by novel low temperature approaches such as a reverse microemulsion method employing different reducing agents like sodium formate or sodium borohydride and polyol reduction methods, followed by heat treatment at moderate temperatures to achieve a high degree of alloying and homogeneity, small and uniform distribution of particle size, high catalytic activity, and good chemical stability. The alloy catalysts are characterized by a variety of physical techniques including diffraction, microscopy, spectroscopy, and electrochemical measurements (cyclic voltammetry, linear polarization, and rotating disk electrode methods). The catalytic activity is evaluated for both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in single cell proton exchange membrane fuel cells and direct methanol fuel cells with hydrogen and methanol fuels. Based on the results, a fundamental understanding of the catalytic mechanisms is developed.Intellectual Merit: The intellectual merit of the proposed activity is to (i) develop a basic scientific understanding of the factors that control the electrocatalytic activity of nanostructured palladium-based alloy catalysts for oxygen reduction reaction and methanol oxidation reaction in fuel cells, and (ii) utilize the knowledge to design and develop new less expensive, more efficient palladium-based catalysts for fuel cells. Palladium-based alloy catalysts designed with a guiding principle are synthesized by controlled, low temperature methods to keep the particle size small and maximize the catalytic activity, screened with cyclic voltammetry, and characterized by a variety of physical, chemical, and electrochemical techniques to establish the catalytic mechanisms involved. The proposed research activity will enhance our fundamental understanding of the structure-property-performance relationships of electrocatalysts and the commercialization prospects of fuel cell technology.Broader Impact: The proposed research provides a broader interdisciplinary training to students in a unique, nationally important area of materials for energy conversion, encompassing materials chemistry and electrochemical science and engineering. The realization of a strong scientific basis in this area can help to design and develop new materials for power sources for portable, automobile, and stationary applications, which would have a profound societal impact. The proposed activity also aims to recruit and train minority and women students and educate K-12 students and the general public about clean energy technologies and materials.