Single Cobalt Sites Dispersed in Hierarchically Porous Nanofiber Networks for Durable and High-Power PGM-Free Cathodes in Fuel Cells |
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| Authors: | Yanghua He Hui Guo Sooyeon Hwang Xiaoxuan Yang Zizhou He Jonathan Braaten Stavros Karakalos Weitao Shan Maoyu Wang Hua Zhou Zhenxing Feng Karren L More Guofeng Wang Dong Su David A Cullen Ling Fei Shawn Litster Gang Wu |
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| Affiliation: | 1. Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY, 14260 USA;2. Department of Chemical Engineering, University of Louisiana at Lafayette, Lafayette, LA, 70504 USA;3. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973 USA;4. Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213 USA;5. Department of Chemical Engineering, University of South Carolina, Columbia, SC, 29208 USA;6. Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261 USA;7. School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, 97331 USA;8. X-ray Science Division, Argonne National Laboratory, Lemont, IL, 60439 USA;9. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831 USA |
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| Abstract: | Increasing catalytic activity and durability of atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction (ORR) cathode in proton-exchange-membrane fuel cells remains a grand challenge. Here, a high-power and durable Co–N–C nanofiber catalyst synthesized through electrospinning cobalt-doped zeolitic imidazolate frameworks into selected polyacrylonitrile and poly(vinylpyrrolidone) polymers is reported. The distinct porous fibrous morphology and hierarchical structures play a vital role in boosting electrode performance by exposing more accessible active sites, providing facile electron conductivity, and facilitating the mass transport of reactant. The enhanced intrinsic activity is attributed to the extra graphitic N dopants surrounding the CoN4 moieties. The highly graphitized carbon matrix in the catalyst is beneficial for enhancing the carbon corrosion resistance, thereby promoting catalyst stability. The unique nanoscale X-ray computed tomography verifies the well-distributed ionomer coverage throughout the fibrous carbon network in the catalyst. The membrane electrode assembly achieves a power density of 0.40 W cm?2 in a practical H2/air cell (1.0 bar) and demonstrates significantly enhanced durability under accelerated stability tests. The combination of the intrinsic activity and stability of single Co sites, along with unique catalyst architecture, provide new insight into designing efficient PGM-free electrodes with improved performance and durability. |
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| Keywords: | electrocatalysis electrospinning fuel cells oxygen reduction single Co sites |
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