Strategies for reconciling tradeoff between conductivity and swelling in alkaline polymer electrolytes membrane

Alkaline polymer electrolytes membrane fuel cells (APEMFC) have been investigated as an alternative to proton-exchange membrane fuel cells (PEMFC) because of their compatibility with nonprecious-metal catalyst, favorability toward fuel oxidation, together with the lower cost, where the charge carrier is OH^- rather than H⁺. However, the performance of APEMFC, especially the conductivity, has thus far lagged that of PEMFC because of the intrinsic lower mobility of OH^- than that of H⁺. The improvement of ion-exchange capacity (IEC) by increasing the grafting degree (GD) of cationic functional groups can, to some extent, solve this issue; however, a high IEC is always accompanied by excessive water uptake, swelling, and backbone degradation. Balancing the ionic conductivity and the dimensional stability in APEs has been a formidable scientific challenge. Here, we reviewed the research progress of the strategies for reconciling the tradeoff between conductivity and dimensional stability. These strategies include physical stratigies, such as blending and filling pores to restain the swelling, chemical cross-linking, enrichment of quaternary ammonium cation groups in the side chains and constructing efficient ionic channels by hydrophilic/hydrophobic phase segregation morphological structure like Nafion^® membranes to enhance the mobility of OH^-. The strategies mentioned above can all realize high ion conductivity and low water uptake and swelling at the same time to some extent.