Improving the performance of quaternized SEBS based anion exchange membranes by adjusting the functional group and side chain structure

Polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) has attracted more and more attention recently for using as the matrix of anion exchange membranes (AEMs) in fuel cells due to its low cost, superior mechanical properties and ether-free total C-C bond backbone. In this work, the short side chain of chloromethyl and long side chain of bromohexanoyl groups are grafted into the SEBS copolymer via the chloromethylation and FriedelCrafts acylation reactions. After quaternized by different nitrogen heterocyclic compounds including 1-methylimidazole (Im), 1-methylpyrrolidine (Mpy), N-methylpiperidine (Pip) and 2-methyl-1-pyrroline (Mpyl), various SEBSCn-x AEMs are prepared. Combing with small molecule model experiment results, Mpy and Pip cations grafted SEBS membranes are confirmed to possess good alkali resistance, while SEBSC1-x membranes with Im and Mpyl cations are not suitable for AEMs due to their poor alkaline stability. Meanwhile, long sidechain cation grafted SEBSC6-x AEMs with lower ion exchange capacity (IEC) values exhibit higher water uptake, ionic conductivity and mechanical strength simultaneously comparing with short side-chain cation grafted SEBSC1-x AEMs. As an example, the SEBSC6-Pip membrane with an IEC of 0.48 mmol g(-1) exhibits a water uptake of 47% at 80 degrees C, an OH- conductivity of 57.7 mS cm(-1) at 80 degrees C, a tensile strength of 52 MPa at room temperature, and a conductivity retention percent of 75% after 600 h in 1 M KOH at 80 degrees C, demonstrating a big potential for the AEM fuel cell application.

Automated summary

SEBS copolymer modified with different nitrogen heterocyclic compounds and cations have been prepared for the fabrication of AEMs in fuel cells. Among them, membranes with Mpy and Pip cations grafting exhibit good alkali resistance, while those with Im and Mpyl cations are not suitable for AEMs due to poor alkaline stability. AEMs with long sidechain cations show higher water uptake, ionic conductivity, and mechanical strength compared to short side-chain cations grafted AEMs.