Self-crosslinked blend alkaline anion exchange membranes with bi-continuous phase separated morphology to enhance ion conductivity

Abstract

Combining two facile methods, spinodal blending and self-crosslinking by chloromethyl groups are jointly utilized in fabricating alkaline anion exchange membranes (AEMs). Highly and moderately chloromethylated poly(ether ether ketone)s and sub-equimolar (to chloromethyl) amounts of 1-methylimidazole are mixed and reacted to form blend AEMs. Nanoscale bi-continuous phase separated morphologies are obtained due to spinodal decomposition. Subsequent heat treatment triggers self-crosslinking of the AEMs arising from residual chloromethyl groups in membranes. Compared with unblended and uncrosslinked AEMs having similar ion exchange capacity (IEC), the ion conductivity of the present AEMs is increased by 45.4% in water and 113% in 95% RH at 60 °C. Dimensional and alkaline stabilities of AEMs are also enhanced by the self-crosslinking, i.e., the swelling ratio decreases by 50.3% at 60 °C and the residual conductivity increases by 26.3% after alkaline treatment in 1 M NaOH at 60 °C. Interestingly, individual spinodal blending or self-crosslinking are found ineffective in overcoming the trade-off between AEM conductivity and stability, while a combination of both methods leads to a simultaneous improvement in conductivity and membrane stability.