Hybrid molecular modeling and experimental study of structure and reaction kinetics at interface between electrode and polymer electrolyte phases

尽管在过去的30年里，人们一直致力于开发更有效和/或低成本的聚合物电解质燃料电池（PEFC）电催化剂和聚合物电解质，但在性能、耐用性和成本方面的基本技术要求尚未得到满足。PEFC技术的主要障碍之一是阴极氧还原反应（ORR）的反应动力学非常缓慢和高活化极化。Pt/Nafion界面处的ORR交换电流密度比Pt/硫酸界面处的ORR交换电流密度低约3个数量级，这表明电催化剂和电解质之间的耦合是至关重要的。这为理论家研究和阐明界面之谜提供了一个完美的案例。因此，提出了一种统一的方法来关注电催化剂/电解质对，而不是单独关注电催化剂和聚合物电解质。智力优势：本研究的目的是阐明导致不同电催化剂/电解质对之间反应动力学数量级差异的基本机制，并建立一种具有成本效益的方法，用于设计和计算机测试更有效和/或低成本的pefc电催化剂/电解质对。为了实现这一目标，将开发一种高通量混合原子模拟方法，并辅以原位x射线吸收分析来确定原子结构或双电层（EDL）结构。该方法将用于评估电催化剂/聚合物电解质界面与电催化剂/液体电解质（如h2so4）界面上的电化学电荷转移和ORR极化。电催化剂和聚合物电解质研究的统一方法是新颖的，有可能提高我们对电催化剂和聚合物电解质之间EDL的基本机制和电荷转移特性的理解。此外，拟议的研究还将促进对所有其他涉及固态电解质的电化学系统的基本理解，如高性能锂离子电池、光电化学电池和超级电容器。更广泛的影响：拟议的工作将(1)通过为研究能量转换过程提供分子建模技术的新工具，加强正在进行的pefc和固态超级电容器的博士研究项目；（二）吸引、鼓励和支持优秀本科生攻读博士学位；(3)将分子模拟的相关信息整合到PI和Co-PI教授的课程中；(4)将信息整合到常规的社区教育任务中；(5)促进女性和少数民族学生的教育。

0933393ZhouProject SummaryAlthough great efforts have been focused on developments of more effective and/or low cost electrocatalysts and polymer electrolytes for polymer electrolyte fuel cells (PEFC) in the last 30 years, the essential technical requirements for performance, durability, and cost have not been satisfied. One of the major barriers for PEFC technology is the very slow reaction kinetics and high activation polarization for the oxygen reduction reaction (ORR) at the cathode. The fact that the ORR exchange current density at the Pt/Nafion interface is about 3 orders of magnitude lower than that at the Pt/sulfuric acid interface suggests that the coupling between an electrocatalyst and an electrolyte is critical. This provides a perfect case for theoreticians to study and elucidate the mystery with respect to interfaces. Therefore, a unified approach is proposed to focus on the electrocatalyst/electrolyte couple rather than the electrocatalyst and polymer electrolyte separately. Intellectual Merits: The objectives of this research are to elucidate the fundamental mechanisms that cause the orders of magnitude differences in reaction kinetics between different electrocatalyst/electrolyte couples, and to establish a cost effective methodology for designing and computer-testing more effective and/or low cost electrocatalyst/electrolyte couples for PEFCs. To reach the objectives, a high throughput hybrid atomistic simulation methodology will be developed and it will be assisted by in situ X-ray absorption analysis to define the atomic structure or electric double layer (EDL) structures. This methodology will be used to evaluate the electrochemical charge transfer and polarization in ORR at the electrocatalysts/polymer electrolyte interface in contrast to the electrocatalysts/liquid electrolyte (e.g.H2SO4) interface. The unified approach in electrocatalyst and polymer electrolyte research is novel and has the potential to improve our understanding of the fundamental mechanisms of the EDL between an electrocatyst and a polymer electrolyte and the charge transfer characteristics. Furthermore, the proposed research will also promote the fundamental understanding of all other electrochemical systems that involve solid-state electrolytes, such as high performance lithium-ion batteries, photoelectrochemical cells, and supercapacitors. Broader impact: The proposed work will (1) enhance ongoing PhD research programs on PEFCs and solid-state supercapacitors by providing new tools of molecular modeling techniques to the study of energy conversion processes; (2) attract, encourage, and support outstanding undergraduate students to pursue a PhD study; (3) integrate the information on molecular simulation into curricula of the courses taught by the PI and Co-PI; (4) integrate the information into regular community education tasks; and (5) promote education of female and minority students.