Alkali-Stable Anion Exchange Membranes Based on Poly(xanthene)

Poly(xanthene)s (PXs) carrying trimethylammonium, methylpiperidinium, and quinuclidinium cations were synthesized and studied as a new class of anion exchange membranes (AEMs). The polymers were prepared in a superacidmediated polyhydroxyalkylation involving 4,4 '-biphenol and 1-bromo-3-(trifluoroacetylphenyl)-propane, followed by quaternization reactions with the corresponding amines. The architecture with a rigid PX backbone decorated with cations via flexible alkyl spacer chains resulted in AEMs with high ionic conductivity, thermal stability and alkali-resistance. For example, hydroxide conductivities up to 129 mS cm-1 were reached at 80 degrees C, and all the AEMs showed excellent alkaline stability with less than 4% ionic loss after treatment in 2 M aq. NaOH at 90 degrees C during 720 h. Critically, the diaryl ether links of the PX backbone remained intact after the harsh alkaline treatment, as evidenced by both 1H NMR spectroscopy and thermogravimetry. Our combined findings suggest that PX AEMs are viable materials for application in alkaline fuel cells and electrolyzers.

Automated summary

Poly(xanthene)s (PXs) with trimethylammonium, methylpiperidinium, and quinuclidinium cations were synthesized and studied as anion exchange membranes (AEMs). These AEMs exhibited high ionic conductivity, thermal stability, and alkali-resistance, making them suitable for alkaline fuel cells and electrolyzers. The polymer architecture with a rigid PX backbone decorated with cations via flexible alkyl spacer chains contributed to these excellent properties.