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How long's too long? Effects of crosslinker length on anion-exchange membrane fuel cells

December 17, 2020
Incheon National University
Anion exchange membrane (AEM) fuel cells (AEMFCs), which produce electricity using hydrogen, are considered an alternative to currently used proton exchange membrane fuel cells. However, AEMs have problems with stability in alkaline conditions, which can be overcome by crosslinking -- but effects of crosslinker length on AEMFC performance are not well understood. Now, scientists have elucidated such effects for oxygen-containing crosslinkers and, using an optimally long crosslinker, produced a novel AEMFC with greater performance.

Many efforts are being made worldwide to replace fossil fuels with greener alternatives. Hydrogen (H2) is a promising option that is currently in the spotlight; it can be used to generate electricity in fuel cells with water generated as the only byproduct. However, the technology is not quite ready for commercialization because proton-exchange membrane fuel cells, the most widely studied type, suffer from high cost and stability issues.

In contrast, anion-exchange membrane (AEM) fuel cells use cheaper catalysts and can offer superior performance. In these cells, hydroxide ions (OH-) are circulated instead of protons through the use of a polymer electrolyte composed of a polymer backbone and ion-conducting groups. One way to improve the properties of such electrolytes is by crosslinking -- physically or chemically linking polymer units to each other through molecular side chains.

Although oxygen-containing crosslinkers improve the stability and ion conductivity of AEMs by virtue of their hydrophilicity, or affinity for water, the effects of crosslinker length, which defines the number of oxygen atoms, are not understood in detail.

To gain deeper insight into this issue, scientists at Incheon National University recently carried out a study where they prepared long AEM polymers with ammonium ion-conducting groups and bound these molecules together using ethylene oxide (EO)-containing crosslinkers of various lengths. Through a wide variety of experiments, they compared AEMs with different crosslinker lengths in terms of their mechanical and thermal properties, water retention capacity, OH- ion conductivity, morphology, and stability. Their findings are published in the Journal of Membrane Science, a top journal in the field of polymer science.

The experiments helped the scientists elucidate the mechanisms by which excessive crosslinker length can ultimately degrade the performance of AEMs. Professor Tae-Hyun Kim, who led the study, explains: "Though it was easy to predict that oxygen-containing crosslinkers would increase hydrophilicity and possibly lead to better ionic conductivity, our results reveal that an excessively large number of repeating oxygen units increases the crystallinity -- or degree of order -- of the resulting material. In turn, this actually reduces hydrophilicity and ultimately compromises many physicochemical properties of the AEM."

After establishing the optimal length for their crosslinker, the researchers prepared an AEM fuel cell and found that the resulting performance was markedly better than when using AEMs without oxygen-containing crosslinkers. Excited about the results, Professor Kim comments: "The main takeaway from our study is that adding molecules with high water affinity, such as ethylene oxide, to crosslinkers of optimal length is a valid strategy to improve the fundamental properties of AEMs and their performance in actual fuel cells."

Although there is still room for improvement before AEM fuel cells can be effectively used in practice and commercialized, this study takes our society a step further towards the popularization of next-generation ecofriendly energy sources.

Story Source:

Materials provided by Incheon National University. Note: Content may be edited for style and length.

Journal Reference:

  1. Seounghwa Sung, T.S. Mayadevi, Kyungwhan Min, Junghwa Lee, Ji Eon Chae, Tae-Hyun Kim. Crosslinked PPO-based anion exchange membranes: The effect of crystallinity versus hydrophilicity by oxygen-containing crosslinker chain length. Journal of Membrane Science, 2021; 619: 118774 DOI: 10.1016/j.memsci.2020.118774

Cite This Page:

Incheon National University. "How long's too long? Effects of crosslinker length on anion-exchange membrane fuel cells." ScienceDaily. ScienceDaily, 17 December 2020. <>.
Incheon National University. (2020, December 17). How long's too long? Effects of crosslinker length on anion-exchange membrane fuel cells. ScienceDaily. Retrieved December 4, 2023 from
Incheon National University. "How long's too long? Effects of crosslinker length on anion-exchange membrane fuel cells." ScienceDaily. (accessed December 4, 2023).

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