Anion exchange membrane (AEM) has been recognized as a promising solid-state electrolyte used in clean energy storage and conversion devices, such as electrolyzers and fuel cells. Great efforts have been made to develop efficient, durable, and low-cost AEMs aiming for wider commercial adoptions. Although ion conductivity could be improved by increasing the ion exchange capacity (IEC) of AEMs, membranes with high IECs tend to show compromised mechanical integrity due to excessive swelling in water. Therefore, an extra step of crosslinking is usually necessary, but it also complicates the material design and increases overall cost. In this presentation, a new and facile synthetic and processing method of preparing crosslinked AEMs, which combines the polymer functionalization and crosslinking in a single step, will be discussed. Polystyrene-b-polybutadiene-b-polystyrene (SBS) was chosen as a starting material because of its good intrinsic mechanical property, excellent film processability, and various chemical modification approaches. Simultaneous polymer functionalization and crosslinking were achieved via UV-initiated cationic ring-opening polymerization of the epoxide groups that were previously introduced to the C=C bonds of SBS. In contrast to traditional bifunctional crosslinkers (e.g. diamines) that result in cationic groups within alkyl chains, our crosslinked AEMs have cationic groups located at the end of flexible spacers. This configuration is expected to favor the formation of well-connected conducting channels and benefit ion transport. The extent of polymer crosslinking/functionalization can be tailored by the feed ratio of epoxidized SBS and 2-(6-bromohexyl)oxirane additives. The resulting AEMs exhibit high hydroxide conductivity (&gt; 0.1 S/cm at 80 oC) with controlled membrane swelling in water (&lt; 35% in hydroxide anion form). They also possess satisfactory chemical stability after immersing in 1M NaOH solution at 80 oC for 500 h. This research work provides an efficient synthetic platform for making mechanically robust next-generation AEMs for electrochemical applications.

Development of mechanically robust crosslinked anion exchange membrane via epoxidized SBS intermediate

ACS Spring Meeting 2021

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