Anion exchange polyelectrolytes for membranes and ionomers

Abstract

Anion exchange membrane fuel cells (AEMFCs) have attracted great interest as a low-cost fuel cell technology for clean energy conversion and utilization for the future. AEMFCs have been considered the most promising succedaneum to proton exchange membrane fuel cells (PEMFCs) for addressing the cost issues associated with PEMFCs due to utilizing non-platinum group metals as electrocatalysts under alkaline conditions (such as Ag, Ni, and Co). Herein, we focus on a critical topic of AEMFCs—-anion-exchange polyelectrolytes (AEPs)—which are essential materials for low-cost AEMFCs. Specifically, AEPs have been used as anion-exchange membranes (AEMs) and binders (or ionomers) in AEMFCs. Years of study have allowed AEMFCs to recently achieve unprecedented progress, specifically in terms of power density and durability. These properties are comparable to or higher thanPEMFCs due to the recent development of high performance AEPs. Currently, most AEPs focused on the application of AEMs, and the importance of ionomer research has not been widely recognized. Moreover, a comprehensive review involving a systematic performance comparison of the state-of-the-art AEMs and ionomers is still lacking, making future research on AEMFCs unclear. This review systematically and comprehensively summarizes the development of AEPs and highlights the importance of cationic species and polymer backbone structures on durability with an emphasis on the importance of ionomer research. We further describe the differences between AEMs and ionomers by comparing the advantages and disadvantages of the state-of-the-art AEMs and ionomers to accurately guide future research on AEMFCs. We cover synthetic methods, degradation mechanisms, strategies to enhance performance, water transport behaviors, structure design criteria, and new challenges for AEMs and ionomers. This review is expected to expand further understanding of AEMs and ionomers and provide a future direction for designing AEMs and ionomers for future AEMFCs.