Anion exchange membranes with dense N-spirocyclic cations as side-chain

To prepare anion exchange membranes (AEMs) with high performances, we tethered the as-synthesized oligomers with dense N-spirocyclic cations (NS) as the side-chain to poly(ether sulfone) (PES). The steric hindrance of spirocyclic structure and electron-donating effect of alkyl spacers significantly enhance the stability of cations in harsh alkaline and high hydration conditions. Correspondingly, the ionic exchange capacity (IEC) of PES–NS–10% only decreased by 13.8% and the conductivity remained 84.3% after being immersed in harsh environment (80 °C, 2 M NaOH) for 864 h. In addition, the high density of N-spirocyclic cations in the side-chain benefits the formation of clear microphase separation, as confirmed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The highest conductivity of 95.5 mS cm-1 was achieved by PES–NS–10% at 80 °C while the corresponding swelling ratio was only 7.69%. Furthermore, the single cell assembled with PES–NS–10% showed a peak power density of 110.1 mW cm-2 at 300 mA cm-2. Durability test of the single cell based on PES–NS–10% under 100 mA cm-2 also demonstrates that the as-prepared AEMs with NS have potential application for fuel cells.