The role of electrolyte/cathode interfacial structure on performance of proton exchange membrane fuel cells

质子交换膜燃料电池是一种可替代的能量转换装置，其可以有效地将化学能转换为电能，以用作运输应用中的动力。这些装置的低效与特定化学过程的能量学有关，并限制了它们的性能。 当前最先进的设备不能同时满足效率、功率输出、成本和耐久性目标。大部分的性能损失被分配到氧还原阴极处的过程，其中功率/效率损失、昂贵的铂催化剂的非最佳利用以及对反应物氧气流相对湿度的敏感性挑战了实际装置的开发。这些损失可以部分归因于Pt催化剂颗粒-聚合物电解质界面的不完美设计。然而，目前的尝试，以改善这个接口的设计是有限的，缺乏基本的理解，它的作用，决定设备的性能。本论文的研究目标是：（1）利用分子动力学和量子力学方法对质子交换膜燃料电池（PEMFC）中的膜/阴极电催化界面进行模拟;（2）描述湿度和电化学电势对该界面结构和氧还原反应动力学的影响;（3）估计由于非理想电解质/电极界面结构而导致的PEMFC性能损失。提出了一种多尺度、集成的分子模拟方法来理解电极/电解质界面结构对氧还原反应速率的影响。分子动力学（MD）将被用来探测该界面的结构作为电极电位和水合作用的函数。量子力学（QM）的方法将被用来量化的元素氧还原反应动力学对这种界面结构的依赖。将开发MD和QM方法应用于电化学界面的方法进展。总的来说，这些方法将建立反应速率作为水合作用和电极电位的函数，这与PEMFC效率和功率输出直接相关。因此，这种接口的结构可以链接到PEMFC的性能损失，从而提供所需的基本结构性能关系，以改善设备的设计。更广泛的影响：这项工作将（1）通过探测这些组件之间的界面，整合目前分别集中在膜材料和电极设计上的能量转换装置分子模拟研究工作;（2）通过培训研究生将分子模拟技术应用于能量转换过程的研究，加强正在进行的研究;以及（3）通过开发该领域的高级课程，将这种培训扩展到研究小组之外;让来自代表性不足群体的本科生在大学生涯的早期使用分子建模技术参与研究。 将开发一门强调能量应用的分子模拟高级课程。 将向技术界提供和宣传为这一课程开发的单元。研究生研究人员将接受先进的技术培训，重点是研究成果的有效交流。此外，拟议研究的组成部分将通过宾夕法尼亚州立大学的既定项目作为研究项目提供，以招募和激励女性和少数民族本科生利用计算技术从事研究工作。

Proton exchange membrane fuel cells are an alternative energy conversion device that may efficiently convert chemical energy to electrical energy for use as motive power in transportation applications. Inefficiencies in these devices are associated with the energetics of specific chemical processes and constrain their performance. The current state-of-the-art devices can not simultaneously meet efficiency, power output, cost, and durability targets. A majority of the performance losses are allocated to processes at the oxygen reduction cathode, where power/efficiency losses, non-optimum utilization of expensive platinum catalyst, and sensitivity to the reactant oxygen stream relative humidity challenge the development of practical devices. These losses can, in part, be attributed to imperfect design of the Pt catalyst particle-polymer electrolyte interface. However, current attempts to improve the design of this interface are limited by a lack of fundamental understanding of its role in dictating device performance. The complexity inherent in this interface and the need to characterize it under operating conditions limit the ability of experimental techniques to link interfacial structure to PEMFC performance.Intellectual Merit: The research objectives of the proposed work are to (1) appropriately model the membrane/cathode electrocatalytic interface in a proton exchange membrane fuel cell (PEMFC) using both molecular dynamics and quantum-mechanical methods; (2) to describe the influence of humidity and electrochemical potential on the structure of this interface and on oxygen reduction reaction kinetics; and (3) to estimate the losses in PEMFC performance due to a non-ideal electrolyte/electrode interfacial structure. A propose multi-scaled, integrated molecular modeling approach to understand the influence of electrode/electrolyte interfacial structure on oxygen reduction reaction rates is proposed. Molecular dynamics (MD) will be used to probe the structure of this interface as a function of electrode potential and hydration. Quantum-mechanical (QM) methods will be used to quantify the dependence of the elementary oxygen reduction reaction kinetics on this interfacial structure. Method advances in both the application of MD and QM methods to the electrochemical interface will be developed. Collectively, these methods will establish the rate of reaction as a function of hydration and electrode potential, which is directly linked to the PEMFC efficiency and power output. Therefore, the structure of this interface can be linked to PEMFC performance losses thus providing the fundamental structure-performance relationships needed to improve device design. Broader Impact: The proposed work will (1) integrate research efforts in the molecular modeling of energy conversion devices currently concentrating separately on membrane materials and electrode design by probing the interface between these components; (2) enhance ongoing research by training graduate students in the application of molecular modeling techniques to the study of energy conversion processes; and (3) to extend this training beyond the perspective research groups through the development of an advanced course in this area; to involve undergraduates from under-represented groups in research using molecular modeling techniques early in their collegiate careers . An advanced course in molecular modeling emphasizing energy applications will be developed. The modules developed for this course will be made available and publicized to the technical community. Graduate student researchers will receive advanced technical training with additional emphasis on the effective communication of research results. Additionally, components of the proposed study will be offered as research projects through established Penn State programs to recruit and motivate women and minority undergraduate students towards research careers utilizing computational techniques.