Block Copolymers for Electrochemical Energy

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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.