Ion Transport by Nanochannels in Ion-Containing Aromatic Copolymers

The search for the next generation of highly ion-conducting polymer electrolyte membranes has been a subject of intense research because of their potential applications in energy storage and transformation devices, such as fuel cells, vanadium flow batteries, membrane-based artificial photosynthesis, water electrolysis, or water treatment processes such as electrodialysis desalination. Nanochannels that contain ionic groups, through which "hydrated" ions can pass, are believed to be of key importance for efficient ion transport in polymer electrolytes membranes. In this Perspective, we present an overview of the approaches to induce ion-conducting nanochannel formation by self-assembly, using polymer architecture such as block or comb-shaped copolymers. The transport properties of ion-containing aromatic copolymers are examined to obtain an insight into the fundamental behavior of these materials, which are targeted toward applications in fuel cells and other electrochemical devices. Challenges in obtaining well-defined nanochannel morphologies, and possible strategies to improve transport properties in aromatic copolymers having structures with the potential to withstand operation in electrochemical/chemical devices, are discussed. Opportunities for the application of ion-containing aromatic copolymer membranes in fuel cells, vanadium flow batteries, membrane-based artificial photosynthesis, electrolysis, and electrodialysis are also reviewed. Research needs for further improvements in ionic conductivity and durability, and their applications are identified.