Mechanically robust microporous anion exchange membranes with efficient anion conduction for fuel cells

Polymers of intrinsic microporosity (PIMs) present an attractive opportunity for developing new types of anion exchange membranes (AEMs) for fuel cell featuring charged subnanometer-sized micropores. But challenges exist to make mechanically robust PIM AEMs due to their high chain rigidity. Imparting more flexibility improves mechanical properties but sacrifices microporosity. Here, a mechanically robust and highly anion conductive PIM AEM (QPIM-1) fabricated by facile animation and quaternization of PIM-1 membrane is reported, and its structure–property relationships are investigated, especially focusing on the microporous structure. High molecular weight alleviates brittleness, as QPIM-1 AEM shows comparable mechanical properties to conventional AEMs, quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO), at a membrane thickness down to ~35 μm and a high ion exchange capacity (IEC) up to ~2.1 mmol g−1. The micropores situated among the rigid and contorted polymer chains evolve into water/ion conduction channels when the membrane is hydrated. This results in improved morphology over dense polymeric AEMs by less hindered ion pathways. QPIM-1 AEMs exhibit superior ion conduction efficiency, which is 2.6–5.3 times that of dense QPPO AEM at similar ion exchange capacities (IECs). A high hydroxide ion conductivity of 57 mS cm−1 at 20 °C is obtained, which is among the highest reported anion conductive PIM-based AEMs. Even though the AEMs are microporous, only slight H2 permeation is observed when hydrated and at high open circuit voltage (OCV) of a single fuel cell.