A mechanically robust anion exchange membrane with high hydroxide conductivity

• Anion exchange membrane with bi-cations containing side chain was designed.
• The densely functionalized side chain was terminated with one unsaturated bond.
• Densely crosslinked network and good nano-phase separation were formed.
• Improved mechanical properties and high hydroxide conductivity were observed.

As a key component of various electrochemical systems, such as alkaline polyelectrolyte fuel cells (APEFCs), flow batteries and electrolyzers, anion exchange membranes (AEMs) need to be both mechanically robust and highly conductive to hydroxide ions. In this work, a polyelectrolyte with a particular polymer structure was designed by combining phase-separation architecture and a crosslinking strategy to improve both the mechanical properties and hydroxide conductivity. The side chain of this type of polyelectrolyte was incorporated by two quaternary ammonium groups and terminated with a cross-linkable unsaturated bond. After being simply heated at 80 °C for 24 h, the crosslinked AEMs exhibited enhanced tensile strength ranging from 23.1 MPa to 14.7 MPa under hydrated conditions. These values are several times higher than the values of conventional AEMs. As a result of the high flexibility and hydrophilicity of the dual-cation-functionalized side chain, an outstanding hydroxide conductivity was observed (43 mS/cm at room temperature and 88.7 mS/cm at 80 °C). Also considering its good dimensional stability and satisfying alkaline tolerance, this strategy combining phase separation architecture and crosslinking has perfectly solved the several obstacles blocking the development of AEMs and thus possesses a great potential for practical application.

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