Nanostructured Palladium-based Alloy Catalysts for Fuel Cells

化石燃料的迅速耗尽和日益增长的环境问题已经在全世界范围内对替代性清洁能源技术产生了巨大的需求。能源是人类在21世纪世纪面临的最大挑战。燃料电池为解决从便携式到汽车到固定电源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，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许多与耐用性，性能和成本相关的材料挑战，阻碍了商业化前景。从2004年国家研究理事会/国家工程院报告和美国物理学会报告中可以看出，对燃料电池材料中化学和物理过程的深刻基本理解对于实现重大突破至关重要，这将导致以可承受的成本提高燃料电池性能。例如，目前使用的铂催化剂的高成本和有限的丰度对燃料电池的商业化前景造成了严重的问题。该提案通过探索新的钯基合金催化剂来解决这一关键问题;钯的成本是铂成本的五分之一。用于氧还原反应（ORR）的纳米结构钯基合金催化剂是基于指导原则设计的，该指导原则涉及将用于首先分裂O-O键以形成吸附氧的良好氧键分裂金属（例如Co）与用于有效地将吸附氧原子还原成氧化物离子的良好氧还原金属（例如Pd）配对。潜在的催化剂组合物确定的循环伏安法（CV）筛选与玻璃碳微电极。由钯和其它金属如Ti、V、Cr、Fe、Co、Ni、Cu、Mo、W、Ru、Au和Pt组成的多金属二元和三元合金组合物通过新颖的低温方法如使用不同还原剂如甲酸钠或硼氢化钠的反相微乳液法和多元醇还原法合成，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、高催化活性和良好的化学稳定性。合金催化剂的特征在于各种物理技术，包括衍射，显微镜，光谱学，和电化学测量（循环伏安法，线性极化，和旋转盘电极方法）。在单电池质子交换膜燃料电池和直接甲醇燃料电池中，以氢和甲醇为燃料，对氧还原反应（ORR）和甲醇氧化反应（莫尔）的催化活性进行了评价。基于这些结果，我们对催化机理有了基本的了解。拟议活动的智力价值是（i）对控制纳米结构钯基合金催化剂在燃料电池中用于氧还原反应和甲醇氧化反应的电催化活性的因素形成基本的科学认识，和（ii）利用这些知识来设计和开发用于燃料电池的新的更便宜、更有效的钯基催化剂。根据指导原则设计的钯基合金催化剂通过受控的低温方法合成，以保持颗粒尺寸小并最大化催化活性，用循环伏安法筛选，并通过各种物理，化学和电化学技术表征以建立所涉及的催化机制。建议的研究活动将提高我们对电催化剂的结构-性质-性能关系的基本理解和燃料电池技术的商业化前景。更广泛的影响：建议的研究为学生提供了更广泛的跨学科培训，在一个独特的，国家重要的能源转换材料领域，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可以帮助设计和开发便携式，汽车和固定应用的电源新材料，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民族学生和女学生，并教育K-12学生和公众了解清洁能源技术和材料。

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.