Novel proton exchange membranes based on sulfonated-phosphonated poly (p-phenylene-co-aryl ether ketone) terpolymers with microblock structures for passive direct methanol fuel cells

The development of fluorine-free proton exchange membranes (PEMs) to improve alcohol resistance and proton/methanol selectivity is a significant research direction for direct methanol fuel cells (DMFCs). In this work, a range of sulfonated-phosphonated poly (p-phenylene-co-aryl ether ketone) terpolymers with microblock structures are prepared by a Ni (0)-catalyzed coupling reaction at high yield. The experimental results reveal that the formation of P-O-P anhydride bridges by self-condensation in a hydrophilic domain can facilitate the connectivity of the proton conducting channels, through a mixed Grotthuss and Vehicle proton transport mechanism, and improve the alcohol resistance of terpolymers at the same time. The terpolymers have high conductivity (> 0.01 S cm(-1)), which is superior to that of neat sulfonated or neat phosphonated aromatic polymers, and high dimensional stability at 80 degrees C and 40% relative humidity. A passive DMFC with a terpolymer membrane provides a high power density of 34.4 mW cm(-2) at 25 degrees C, which is higher than that for l-SPP-co-PAEK 1.80 (27.1 mW cm(-2)) and Nafion (R) 115 (29.3 mW cm(-2)). By controlling the ratio of phosphonic acid or sulfonic acid to regulate ion aggregation behavior and further construct connected (or cluster-free) proton channels, a new insight into the design PEMs with high proton/methanol selectivity is provided.