Magnetic field-oriented ferroferric oxide/poly(2,6-dimethyl-1,4-phenylene oxide) hybrid membranes for anion exchange membrane applications.

Abstract

Concentrating on the ion conductivity of anion exchange membranes (AEMs), we present a magnetic-field-oriented strategy to address the insufficient ion conductivity and the lifetime problem of AEMs used in alkali membrane fuel cells (AMFCs). Magnetic ferroferric oxide (Fe3O4) is functionalized with quaternary ammonium (QA) groups to endow the QA-Fe3O4 with ion-exchange ability. A series of aligned QA-Fe3O4/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) hybrid membranes were fabricated by doping QA-Fe3O4 in a triple-ammonium-functionalized PPO (TA-PPO) solution in an applied magnetic field. The structure of aligned QA-Fe3O4 in the TA-PPO membrane is clearly observed by using a scanning electron microscope (SEM). More importantly, the aligned QA-Fe3O4 constructs successive and effective ion-transport channels in the QA-Fe3O4/TA-PPO membrane, which dramatically improves the ion conductivity of the membranes. Notably, the magnetic-field-induced ion channels (MICs) are different from microscopic phase-induced ion channels (PICs). These MICs display much shorter ion transport distances and broader water channels than traditional PICs in AEMs. The aligned QA-Fe3O4/TA-PPO hybrid membrane displays a further 55% increase in ion conductivity after magnetic-field orientation compared to the normal QA-Fe3O4/TA-PPO membrane. Surprisingly, the aligned QA-Fe3O4 also improves the alkali stability and fuel cell performance of the hybrid membrane. The aligned 6%-QA-Fe3O4/TA-PPO hybrid membrane realizes a maximal power density of 224 mW cm-2. In summary, this work provides a novel and effective method to prepare high-performance AEMs.