Ion and Water Transports in Double Gyroid Nanochannels Formed by Block Copolymer Anion Exchange Membranes

Overview & Synopsis

Mechanically improved polymeric membranes with high ionic conductivity (IC) and good permeability are highly desired for next-generation anion exchange membranes (AEMs) in order to reduce Ohmic losses and enhance water management in alkaline membrane fuel cells. To move towards the fabrication of such high-performance membranes, the creation of hydrophilic ion-conducting double gyroid (DG) nanochannels within block copolymer (BCP) AEMs is a promising approach. However, this attractive solution remains difficult to implement due to the complexity of constructing a well-developed ion-conducting DG morphology across the entire membrane thickness. To deal with this issue, water permeable polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) membranes with ion-conducting DG nanochannels were produced by combining a solvent vapor annealing (SVA) treatment with a methylation process. Here, the SVA treatment enabled the manufacture of DG-forming BCP AEMs while the methylation process allowed for the conversion of pyridine sites to N-methylpyridinium (NMP+) cations via a Menshutkin reaction. Following this SVA-methylation method, the IC value of water-permeable (~384 L h−1 m−2 bar−1) DG-structured BCP AEMs in their OH−counter anion form was measured to be of ~2.8 mS.cm−1 at 20 °C while a lower IC value was probed, under the same experimental conditions, from as-cast NMP+-containing analogs with a non-permeable disordered phase (~1.2 mS.cm−1).