Block Copolymers for Electrochemical Energy

在全球范围内，我们正面临一个迫在眉睫的挑战，即用可再生能源取代基于石油的能源。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)中用作固态电解质具有很高的应用价值。与标准质子交换膜(PEM)设备相比，阴离子交换膜(AEM)的碱性环境为催化剂和分离材料的低成本提供了机会，并改善了水管理，减少了气体交叉。这项研究计划的总体目标是通过研究嵌段共聚物AEMS作为高性能固体电解质来促进电化学能源技术的发展。在过去的十年中，AEMS的导电性有了显着的提高，但仍不能与PEMS相提并论。聚合物的形态对离子导电性有很大影响。特别是，嵌段共聚物中的微相分离允许AEMS中的纳米结构形态，从而显著提高导电性。该项目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。为了促进长程有序，将对聚合物的微相分离强度、离子组成和加工条件进行研究。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。要实现长寿命，需要聚合物主链和阳离子在80-95°C的碱性条件下保持长期稳定。众所周知，氢氧离子的高亲核性和碱性在典型的氢氧化物导电AEM中触发了多条降解路径。该计划的第二个目标是探索能够克服膜碱不稳定问题的聚合物体系结构。开发具有优异的耐碱性化学性能的新型主链和阳离子组合对于实现持久的电化学能量转换仍然至关重要。异地测试对于电化学应用是非常重要的，因为设备变化很大，无法进行高通量的现场测量，耐久性测试的耗时性质(例如，2000小时)，以及许多其他考虑因素(例如，离聚体/催化剂的相互作用)。目前的异地测试通常使分离器材料看起来稳定，但AEM燃料电池耐久性测试显示仅在100-200小时后性能急剧下降。该计划的第三个目标是开发标准化的异地AEM耐久性测试，以准确地与现场设备性能相关联。发展全面评估所有相关AEM性能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.