Nanoscale Structure–Conductivity Relationships in Hydrated Anion Exchange Membranes with Aromatic Backbones

Anion exchange membranes (AEMs) are attractive for fuel cells and electrolyzers because their operation enables the use of abundant, lower-cost non-PGM catalysts. However, state-of-the-art AEMs often struggle to deliver sufficiently high ion conductivity and stability across humidity and temperature, motivating structure-guided designs. Here, we investigate hydrated nanostructures and ion transport in several AEMs with different aromatic repeating units, using small-angle X-ray scattering (SAXS) and broadband dielectric spectroscopy under varied humidity and temperature conditions. SAXS reveals distinct nanophase separation and well-defined hydrophilic domains that vary with AEM backbone and become most pronounced at high relative humidity. The anion conductivity increases with ion-exchange capacity at high water contents, facilitated by nanoscale structures containing hydrated ion transport pathways. By correlating nanoscale morphology with conductivity across variable humidity for multiple AEM backbones, this study clarifies key structure–property relationships that govern ion transport and proposes design principles for next-generation AEMs with enhanced performance in electrochemical energy systems such as fuel cells and electrolyzers.