Branched Poly(arylene ether ketone sulfone)s with Ultradensely Sulfonated Branched Centers for Proton Exchange Membranes: Effect of the Positions of the Sulfonic Acid Groups

Branchedsulfonated polymers present considerable potential forapplication as proton exchange membranes, yet investigation of branchedpolymers containing sulfonated branched centers remains to be advanced.Herein, we report a series of polymers with ultradensely sulfonatedbranched centers, namely, B-x-SPAEKS, where x represents the degree of branching. In comparison withthe analogous polymers bearing sulfonated branched arms, B-x-SPAEKS showed a reduced water affinity, resulting in lessswelling and lower proton conductivity. The water uptake, swellingratio (in-plane), and proton conductivity of B-10-SPAEKS at 80 degrees Cwere 52.2%, 57.7%, and 23.6% lower than their counterparts, respectively.However, further analysis revealed that B-x-SPAEKSfeatured significantly better proton conduction under the same watercontent due to the formation of larger hydrophilic clusters (similar to 10nm) that promoted efficient proton transportation. B-12.5-SPAEKS exhibiteda proton conductivity of 138.8 mS cm(-1) and a swellingratio (in-plane) of only 11.6% at 80 degrees C, both of which were superiorto Nafion 117. In addition, a decent single-cell performance of B-12.5-SPAEKSwas also achieved. Consequently, the decoration of sulfonic acid groupson the branched centers represents a very promising strategy, enablingoutstanding proton conductivity and dimensional stability simultaneouslyeven with low water content.