Covalent organic framework–based porous ionomers for high-performance fuel cells

Lowering platinum (Pt) loadings without sacrificing power density and durability in fuel cells is highly desired yet challenging because of the high mass transport resistance near the catalyst surfaces. We tailored the three-phase microenvironment by optimizing the ionomer by incorporating ionic cov...

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Published in:Science (American Association for the Advancement of Science) 2022-10, Vol.378 (6616), p.181-186
Main Authors: Zhang, Qingnuan, Dong, Shuda, Shao, Pengpeng, Zhu, Yuhao, Mu, Zhenjie, Sheng, Dafei, Zhang, Teng, Jiang, Xin, Shao, Ruiwen, Ren, Zhixin, Xie, Jing, Feng, Xiao, Wang, Bo
Format: Article
Language:English
Subjects:
Catalysts
Fuel cells
Fuel technology
Gas transport
Ionomers
Platinum
Proton exchange membrane fuel cells
Sulfonic acid
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Summary:Lowering platinum (Pt) loadings without sacrificing power density and durability in fuel cells is highly desired yet challenging because of the high mass transport resistance near the catalyst surfaces. We tailored the three-phase microenvironment by optimizing the ionomer by incorporating ionic covalent organic framework (COF) nanosheets into Nafion. The mesoporous apertures of 2.8 to 4.1 nanometers and appendant sulfonate groups enabled the proton transfer and promoted oxygen permeation. The mass activity of Pt and the peak power density of the fuel cell with Pt/Vulcan (0.07 mg of Pt per square centimeter in the cathode) both reached 1.6 times those values without the COF. This strategy was applied to catalyst layers with various Pt loadings and different commercial catalysts. In proton exchange membrane fuel cells, the Nafion ionomer usually overencapsulates and inhibits the platinum catalyst and can impede gas transport in the catalyst layer. Q. Zhang et al . showed that adding a sulfonated covalent organic framework (COF) to Nafion could improve the activity based on platinum by up to 60% (see the Perspective by Ma and Lutkenhaus). The hexagonal pores of the COF improve gas transport, and the sulfonic acid groups anchored on the pore walls decrease binding to platinum, which inhibits its activity. —PDS Adding a sulfonated ionic covalent organic framework into the Nafion ionomer improves gas transport to the catalyst layer.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.abm6304