3 years ago

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

Nitrogen-Coordinated Single Cobalt Atom Catalysts for Oxygen Reduction in Proton Exchange Membrane Fuel Cells
Sooyeon Hwang, Maoyu Wang, Yuyan Shao, Hanguang Zhang, Karren L. More, Jingyun Wang, Jacob S. Spendelow, David A. Cullen, Yanghua He, Gang Wu, Xiao Xia Wang, Dong Su, Zhenxing Feng, Mark H. Engelhard, Yung-Tin Pan
Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN4 coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm−2). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN4 active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates. A nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks with accurately controlled Co contents. Atomic CoN4 sites are observed with advanced electron microscopy combined with X-ray absorption spectroscopy. Due to the high density of atomically dispersed Co sites, the catalyst achieves respectable activity and stability in acidic proton exchange membrane fuel cells.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201706758

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