Abstract
Hydrogen, as a clean energy carrier, is promising to alleviate the dependence on fossil fuels and contributing to carbon-neutrality. Alkaline water electrolyzers (AEMs) and proton exchange membrane water electrolyzers (PEMWEs) have realized commercialization to produce pure hydrogen, while high corrosiveness resulting from concentrated KOH aqueous solution and low hydrogen production efficiency of AWEs, as well as high cost resulting from platinum group metal (PGM) catalysts of PEMWEs enforced to develop the alternatives. Anion exchange membrane water electrolyzers (AEMWEs) which combine the advantages of AWEs and PEMWEs have been regarded as attractive and effective electrochemical devices as emerging water electrolyzers. Over the decades, the catalysts and AEMs have been widely studied to improve the performance and durability of AEMWEs. However, ionomers in the catalyst layers, has been largely overlooked, while ionomers play roles in binding catalyst particles and permeating produced hydrogen and oxygen.Herein, we developed anion exchange ionomers (QC6xBA and QC6xPA) with high gas permeability and dimensional stability by introducing bulky cyclohexyl (C6) groups into polymer backbones. Among synthesized polymers, QC650BA-2.1 (target ion exchange capacity, IEC: 2.1 mmol g-1) with 50 mol% C6 composition was the most gas permeable, having 16.6-fold higher H2 permeability and 22.3-fold higher O2 permeability than QC60BA-2.1 without C6 groups. Meanwhile, QC650BA-2.1 was also more dimensionally stable, the through-plane swelling ratio decreased to 12.5% (QC650BA-2.1) from 31.1% (QC60BA-2.1). Applying QC650BA-2.1 as the anode ionomer and PGM-free Ni0.8Co0.2O1) as anode catalyst, the water electrolysis cell showed 2 times higher performance (2 A cm-2 at 1.69 V) than the cell using our previous QPAF-4-2.02) ionomer. During 1000 h durability test at 1.0 A cm-2, the QC650BA-2.1 cell showed ignorable change of cell voltage with decay rate of 1.1 μV h-1 after initial voltage increase. These results indicated using high gas permeable and dimensionally stable ionomer is significantly effective to enhance the performance and durability of AEMWE.Reference1) Ono, T. Kimura, A. Takano, K. Asazawa, J. Miyake, J. Inukai, K. Miyatake, J. Mater. Chem. A 2017,5, 24804.2) Shi, T. Tano, D. A. Tryk, M. Yamaguchi, A. Iiyama, M. Uchida, K. Iida, C. Arata, S. Watanabe, K. Kakinuma, ACS Catal. 2022, 12, 14209.
Published Version
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