Hierarchical Fe3O4@LDH-incorporated composite anion exchange membranes for fuel cells based on magnetic field orientation

The trade-off between ionic conductivity and mechanical properties is the key issue facing anion exchange membranes (AEMs) at present. Herein, a new strategy combing three-dimensional (3D) hierarchical nanoarchitecture and magnetic field orientation was proposed to prepare imidazolium-functionalized poly(2,6-dimethyl phenylene oxide) (ImPPO)-based composite AEMs with simultaneously improved ionic conductivity and mechanical strength. Magnetic Fe3O4@LDH microspheres using Fe3O4 as the core and two-dimensional lamellar anion conductor, layered double hydroxide (LDH), as the shell were prepared through a simple co-precipitation method. The as-prepared Fe3O4@LDH was then incorporated into ImPPO matrix and induced by an external magnetic field to fabricate Fe3O4@LDH-orientated composite AEMs. The hierarchical-structured Fe3O4@LDH can not only effectively avoid the stacking of LDH laminates and thus fully play the ion conduction ability of LDH, but also contribute to the formation of continuous OH− ion transport pathway in the composite system after magnetic field induction. The magnetic-field-oriented membrane with 1% Fe3O4@LDH doping exhibited ionic conductivity of 128.9 mS cm−1 at 80 °C, which was 43.1% higher than that of pure ImPPO. Moreover, the high dry strength (30.7 MPa) and satisfactory wet strength and flexibility of the composite membrane were also obtained. The assembled direct methanol fuel cell demonstrated a peak power density of 11.7 mW cm−2, and showed an OCV retention of as high as 94.7% after continuous operation for 100 h, indicating their great potential for fuel cell applications.