Search

Tuning the hydrophilic/hydrophobic nanophase-separated morphology to enhance the conductivity is a considerable challenge in the field of anion exchange membranes (AEMs). Here, a series of novel aliphatic-aromatic copolymer AEMs were designed by embedding flexible alkyl chains of different lengths into rigid main chain of poly(ether sulfone). Compared to traditional aromatic polymer, the aliphatic-aromatic copolymers had more flexible main chains and longer hydrophobic segments, both of which promoted the nanophase separation and the formation of ionic clusters. Increasing aliphatic chain length made the ionic clusters larger and more interconnected, but too long aliphatic chain led to the formation of smaller ionic clusters because the ionic groups were far away from each other. An optimum length of the aliphatic chain (8 C) existed for the nanophase-separated morphology with the biggest ionic clusters (around 8 nm), with which the membrane showed the highest conductivity. A peak power density of 159 mW cm−2 was obtained for the cell incorporating the 8 C membrane. Based on these, this study reveals a new direction to create a tunable nanophase-separated morphology for high-performance AEMs.

Inadequate hydroxide conductivity of anion exchange membrane (AEM) is one of the obstacles restricting practical application of anion exchange membrane fuel cell. In this work, we report the design, fabrication and properties of AEMs based on bent-twisted non-coplanar block copolymer. The bent-twisted polymer backbone creates high free volume size so that hydroxide ion transport is facilitated. The free-volume effect can also facilitate microphase separation due to enhanced chain segment motion. With the free-volume holes working synergistically with microphase-separation enabled ion channels, the membrane showed a high conductivity (35 mS cm−1 at room temperature) at a relatively low ion exchange capacity (IEC, 1.25 meq g−1); it also exhibited a good dimension stability, the swelling ratio being 4.7% at room temperature and kept virtually unchanged with temperature because of relatively low IEC. A H2/O2 fuel cell employing the fabricated AEM yielded a high power density (262 mW cm−2 at 50 °C). Our work opens up a new route to fabrication of highly conductive AEM with relatively low IEC.

Hydroxide exchange membrane fuel cells (HEMFCs) receive growing interest due to the usability of non-precious metal catalysts in the basic operating environment. The applications of HEMFCs are hindered by the trade-off between high hydroxide conductivity and good dimensional stability of the HEMs. Here, a novel poly(2,6-dimethyl-1,4-phenylene oxide) with imidazolium-terminated long side chains (PPO-COC 5 H 10 -Im) was synthesized by simple and controllable acetylation reaction of PPO and 6-bromohexanoyl chloride in a moderate condition (at room temperature), followed by the Menshutkin reaction with 1,2-dimethylimidazole. The introduction of long chains between imidazolium groups and polymer main chains facilitates the formation of good hydrophilic/hydrophobic micro-phase separation structure, which is illustrated by TEM. The hydroxide effective mobility in PPO-COC 5 H 10 -Im membrane is almost 2-fold that in short side chain imidazolium functionalized PPO (PPO-CH 2 -Im) membrane at a certain IEC. Given similar swelling ratios (25% vs. 27%), PPO-COC 5 H 10 -Im membrane shows much higher hydroxide conductivity than PPO-CH 2 -Im membrane (62 vs. 42 mS cm −1 ) at 60 °C. It indicates that the PPO-COC 5 H 10 -Im membranes prepared here exhibits highly enhanced conductivity without sacrificing the dimensional stability.