Imaging Morphology, Ion Conductance and Degradation Processes in Energy Materials on the Nanometer Scale Using Tunneling Atomic Force Microscopy

提案编号：1608914 PI：Buratto，S.利用隧道原子力显微镜在纳米级能源材料中的成像形态、离子电导和降解过程聚合物电解质膜(PEM)是燃料电池和氧化还原液流电池等电化学设备中的关键部件。这些设备能够高效地生产清洁能源，与在没有风能或太阳的情况下使用风能或太阳能的间歇性可再生发电技术相结合，还可以将电力以化学能的形式储存起来，以储存能量。质子交换膜通常由具有疏水主链的聚合物和以亲水官能团封端的侧链组成。当这种聚合物被浇铸在薄膜中制成膜时，疏水和亲水部分之间的相分离导致了一个由亲水通道和疏水结构域组成的随机纳米网络，离子通过该网络传输到膜中，疏水结构域赋予膜机械强度。目前正在开发新的膜化学，特别是碱性电解质膜，但需要从表征工作中获得反馈，特别是在纳米尺度上，以便了解离子电导及其对孔网络结构的依赖。另一个关键问题是膜在运行过程中如何降解，这会影响设备的性能。该项目解决了对这些类型的电化学装置中如何发生退化的基本了解的需要。所获得的知识将有助于关闭膜结构设计与其合成功能之间的反馈回路。从事这项研究的学生将了解替代电源，帮助优化膜功能，并为下一代膜材料的开发提供有价值的见解和灵感。该项目利用一套实验方法，利用轻击(或交流)模式原子力显微镜(AFM)和导电探针AFM(CAFM)来探测质子传导膜(如PEM)中的孔连通性和离子传输。首席调查员和他的研究小组开发了这些技术。在本项目中，这些仪器被改装并应用于传输氢氧化物离子的碱性电解质膜的研究。在碱性条件下，氧还原半反应显著改善了动力学，不需要贵金属催化剂。该项目的变革性特征包括在纳米尺度上表征PEM膜的形态和氢氧离子电导，以提供形态和电导之间的联系。该项目还包括在与碱性燃料电池截然不同的操作条件下，研究利用质子导电膜的钒氧化还原液流电池中的离子域形态和连通性。这些实验探索了膜的孔网络结构与电解液浓度、钒离子对膜的渗透程度以及膜表面在水和热中的长时间暴露的依赖关系。最终目标是基本了解离子传导，即碱性燃料电池和钒液流电池中负责传输的化学区域的大小和分布。在这两个系统中，离子电导将作为(1)设备操作条件、(2)膜类型和(3)膜降解和分解程度的函数被系统地研究。

Proposal Number: 1608914 PI: Buratto, S.Imaging Morphology, Ion Conductance and Degradation Processes in Energy Materials on the Nanometer Scale Using Tunneling Atomic Force MicroscopyPolymer electrolyte membranes (PEMs) are key components in electrochemical devices such as fuel cells and redox flow batteries. These devices are capable of producing clean energy with high efficiency and are useful in tandem with intermittent renewable electricity generation technologies using wind or solar when the wind or sun is not available and also to store electricity in the form of chemical energy for energy storage. PEMs are, in general, composed of a polymer with a hydrophobic backbone and side chains terminated with hydrophilic functional groups. When this polymer is cast in films to make the membrane, phase separation between the hydrophobic and hydrophilic segments results in a random nanoscale network of hydrophilic channels through which ions are transported and hydrophobic domains that give the membrane mechanical strength. Novel membrane chemistries are currently under development, especially alkaline electrolyte membranes, but require feedback from characterization efforts, especially on the nanometer scale, in order to understand ion conductance and its dependence on the pore network structure. Another key question is how the membrane degrades during operation and that impacts the performance of the device. This project addresses this need for fundamental understanding on how degradation occurs in these types of electrochemical devices. Knowledge gained will help to close the feedback loop between designing the membrane's structure and its resultant function. Students working on this research will learn about alternative power sources, help optimize membrane function, and provide valuable insight and inspiration into the development of the next-generation membrane materials. This project leverages a suite of experimental methods that utilize tapping (or AC) mode atomic force microscopy (AFM) and conductive probe AFM (cAFM) to probe the pore connectivity and ion transport in proton-conducting membranes such as PEMs. The Principal Investigator and his research group have developed these techniques. In this project, the tools are adapted and applied to the study of alkaline electrolyte membranes, which transport hydroxide ions. Under alkaline conditions, the oxygen reduction half-reaction has significantly improved kinetics, obviating the need for precious metal catalysts. This project's transformative feature includes the characterization of PEM membrane morphology and hydroxide-ion conductance on the nanometer length scale to provide a link between morphology and conductance. The project also includes the investigation of the ion domain morphology and connectivity in vanadium redox flow batteries that utilize proton-conducting membranes under drastically different operating conditions than the alkaline fuel cells. These experiments probe the dependence of the pore network structure on the electrolyte concentration, the degree of vanadium ion penetration into the membrane and the prolonged exposure of the membrane surface to water and heat. The ultimate goal is fundamental understanding of ion conduction, in terms of the size and distribution of the chemical domains responsible for the transport in both alkaline fuel cells and vanadium flow cell batteries. In both systems, ion conductance will be studied systematically as a function of (1) the device operating conditions, (2) the membrane type, and (3) the degree of membrane degradation and decomposition.