Block Copolymers for Electrochemical Energy

在全球范围内，我们正面临着用可再生能源替代石油能源的迫在眉睫的挑战。离子导电聚合物膜在电化学能源技术（如燃料电池、电解槽、电池）中作为固态电解质的应用备受关注。相对于标准质子交换膜（PEM）装置，阴离子交换膜（AEM）的碱性环境为更低成本的催化剂和分离器材料提供了机会，并改善了水管理和减少了气体交叉。该研究计划的总体目标是通过研究嵌段共聚物AEMs作为高性能固态电解质来推进电化学能源技术。在过去十年中，AEMs的导电性显著提高，但仍无法与PEMs相提并论。聚合物形态对离子电导率有显著影响。特别是，嵌段共聚物中的微相分离允许在AEMs中实现纳米结构形态，从而大大提高导电性。该计划的第一个目标是探索新型阴离子导电嵌段共聚物的形态和电导率之间的结构-性能关系。研究了微相分离的强度、离子组成和聚合物的加工条件，以促进长程有序。AEMs在碱性介质中有限的化学和机械稳定性仍然是电化学能源技术的主要障碍。实现较长的设备寿命要求聚合物主链和阳离子在80-95°C的碱性条件下长期保持稳定。众所周知，在典型的氢氧根导电AEM中，氢氧根离子的高亲核性和碱性引发了多种降解途径。该计划的第二个目标是探索聚合物结构，将克服膜碱不稳定性的问题。开发具有优异耐碱性的新型骨架和阳离子组合对于实现持久的电化学能量转换至关重要。非原位测试对于电化学应用具有重要意义，因为存在显著的设备变化、无法进行高通量原位测量、耐久性测试耗时（例如，2000小时）以及许多其他考虑因素（例如，离聚体/催化剂相互作用）。目前的非原位测试通常会使隔膜材料看起来很稳定，但AEM燃料电池耐久性测试显示，仅在100-200小时后，性能就会急剧下降。该项目的第三个目标是开发标准化的非原位AEM耐久性测试，以准确地与原位设备性能相关联。开发全面评价所有相关AEM性质的方法对实现碱性电化学技术具有重要意义。

Globally, we are facing an imminent challenge to replace petroleum-based energy with renewable alternatives. Ion-conducting polymer membranes are of high interest for utilization as solid-state electrolytes within electrochemical energy technologies (e.g., fuel cells, electrolyzers, batteries). Relative to standard proton exchange membrane (PEM) devices, the alkaline environment of anion exchange membrane (AEM) corollaries offers the opportunity for lower cost catalysts and separator materials, as well as improved water management and reduced gas crossover. The overall objective of this research program is to advance electrochemical energy technologies through investigation of block copolymer AEMs as high-performance solid-state electrolytes. Conductivity of AEMs has increased significantly over the last decade but is still not on par with PEMs. Polymer morphology has a significant impact on ion conductivity. In particular, microphase separation in block copolymers allows for nanostructured morphologies in AEMs that substantially enhance conductivity. The first objective of this program is to explore the structure-property relationship between morphology and conductivity in novel, anion-conducting block copolymers. The strength of microphase separation, the ionic composition, and the processing conditions of the polymer will all be investigated in order to promote long-range order. Limited chemical and mechanical stability of AEMs in alkaline media remains a major hindrance for electrochemical energy technologies. Achieving long device lifetimes requires that the polymer backbone and cations remain stable long-term in alkaline conditions at operating temperatures of 80-95 °C. It is well known that the high nucleophilicity and basicity of hydroxide ions triggers multiple degradation pathways in the typical hydroxide-conducting AEM. The second objective of this program is to explore polymer architectures that will overcome issues of membrane alkali instability. The development of new backbone and cation combinations with superior alkaline chemical resistance remains crucial to the implementation of long-lasting electrochemical energy conversion. Ex-situ testing is of major importance for electrochemical applications because of significant device variation, inability to perform high-throughput in-situ measurements, time-consuming nature of durability testing (e.g., 2000 h), and many other considerations (e.g., ionomer/catalyst interactions). Current ex-situ testing often makes separator materials appear stable, but AEM fuel cell durability tests show dramatic drops in performance after only 100-200 h. The third objective of this program is to develop standardized ex-situ AEM durability tests that accurately correlate to in-situ device performance. Developing methods to fully evaluate all pertinent AEM properties has major implications for the realization of alkaline electrochemical technologies.