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

Abstract

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).