Abstract:

Polymer electrolytes are one of the key materials in fuel cells. Alkaline exchange membranes (AEMs), which can transport OH ions, have been intensive studied by many research groups. Alkaline environment can facilitate the reduction of oxygen molecules and therefore the non-precious metal catalyst can be used. However, AEMs are still facing some problems. The key problems of AEMs include the insufficient OH conductivity, the relative insufficient alkaline stability and poor mechanical properties. In this mini review, we discussed recent advances in literatures in AEM field, reviewed the strategy to improve the alkaline stability and OH conductivity. We discussed the performance and hydroxide stability of the widely reported cationic head groups, including the quaternary ammonium, imidazolium, spirocyclic quaternary ammonium, pyrrolidinium. Also the function of construction of cross-linked structures, optimization of polymer backbones, and the function of protective groups were discussed. The influence mechanisms of various factors on the alkaline stability are discussed emphatically. In conclusion, AEMs with high alkaline and high OH conductivity can be achieved by constructing the structure of hydrophilic/hydrophobic phase separation, cross-linked structures, or by optimizing polymer backbones with different structural cationic groups.

Key words: fuel cell, ion exchange membrane, polymer electrolyte, OH conductivity, alkaline stability