Magnetic field-assisted widened short-range ion channels to facilitate ion conductivity for alkaline anion exchange membrane fuel cell

Abstract

The current anion exchange membranes (AEMs) face the “trade-off” between conductivity and alkali resistance. Here, a new strategy integrating controlled radical polymerization, click chemistry, and magnetic field orientation was proposed to establish widened short-range ion transport channels for improving both the conductivity and stability of AEM. Poly[1,2-dimethyl-3-(4-vinylbenzyl)imidazolium chloride] (PImIL) containing imidazolium cations were grafted from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and magnetic carbon nanotubes (M-CNTs) via ARGET ATRP and RAFT polymerization to synthesize the comb-shaped PPO-PImIL and hybrid M-CNTs@PImIL, respectively. Then, an external magnetic field assists in establishing ionized organic-inorganic hybrid co-crosslinked networks with widened short-range ion transport channels via a click reaction, which endows the hybrid AEM with excellent conductivity, dimensional stability, and mechanical strength. The magnetic-field-oriented hybrid AEM, with 5 wt% M-CNTs@PImIL doping and an ion exchange capacity (IEC) of 2.81 mmol/g, exhibits an ionic conductivity of 195.8 mS/cm at 80 °C, which is 2.5 times that of PPO-PImIL. Meanwhile, the enhanced interfacial compatibility and co-crosslinked networks also endow the hybrid AEM with acceptable tensile strength (22.8 MPa) and sufficient thermal stability (higher than 200 °C). Combined with the steric hindrance offered by CNTs and hydrophobic alkyl chain spacers for cationic groups, the alkaline stability is also improved. Ultimately, this hybrid AEM demonstrates outstanding fuel cell performance, achieving a maximum power density of about 654.6 mW/cm² and exhibiting desirable durability with a voltage decay rate of 0.30 mV/h. In summary, this work provides a novel and effective strategy to prepare AEM with excellent overall performance for the application in AEMFCs.