Crosslinked PAEK-based nanofiber reinforced Nafion membrane with ion-paired interfaces towards high-concentration DMFC

Abstract

To increase the energy density of DMFC system, increasing the methanol concentration is an excellent solution. However, the severe methanol crossover problem limits the application of Nafion in DMFCs with a highly concentrated methanol solution. Here, we proposed a feasible approach to overcome this challenge where Nafion membrane was reinforced with a covalently crosslinked quaternized poly (arylene ether ketone) (PAEK) nanofiber mat for establishing acid-base ion-paired interfaces between them. Firstly, the bromomethylated PAEK precursor was prepared into a three-dimensional fibrous support material using electrospinning. The nanofibers were then quaternized and covalently crosslinked to embed in the Nafion matrix while maintaining their fiber morphology. During the membrane fabrication, the ion-paired interfaces were established between the –N(CH3)3+ on the nanofibers and –SO3- groups of Nafion matrix. The strong ion-paired interaction resulted in low membrane swelling and methanol permeability. TEM confirmed that the hydrophilic ionic clusters were aggregated with controllably distribution along the nanofibers to create long-range and efficient proton transport channels. Therefore, the hybrid membrane F-CQPAEK@Nafion-1.0 showed a high proton conductivity of 0.21 S cm−1 at 80 °C. In 2 M DMFC, the maximum power density (PDmax) of this membrane reached 119.38 mW cm−2, 2.78 times higher than that of recast Nafion. In 10 M DMFC, the PDmax of this hybrid membrane reached 65.31 mW cm−2, which was 3.54 times higher than that of recast Nafion. The results illustrate the possibility of running Nafion-based hybrid membranes in DMFCs with a broad operational flexibility from low concentration to high concentration methanol solutions.