Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells

• Published in: Nature energy 2022-07, Vol.7 (7), p.652-663
• Main Authors: Liu, Shengwen, Li, Chenzhao, Zachman, Michael J., Zeng, Yachao, Yu, Haoran, Li, Boyang, Wang, Maoyu, Braaten, Jonathan, Liu, Jiawei, Meyer, Harry M., Lucero, Marcos, Kropf, A. Jeremy, Alp, E. Ercan, Gong, Qing, Shi, Qiurong, Feng, Zhenxing, Xu, Hui, Wang, Guofeng, Myers, Deborah J., Xie, Jian, Cullen, David A., Litster, Shawn, Wu, Gang
• Format: Article
• Language: English
• Subjects: 639/301/299/886; 639/4077/893; 639/4077/909/4086; Accelerated tests; Ammonia; Carbon; Catalysts; Chemical synthesis; Durability; Economics and Management; Electrodes; Energy; Energy Policy; Energy Storage; Energy Systems; Fuel cells; Fuel technology; Heat treatment; Heat treatments; High temperature; Hydrogen fuels; Iron; Nitrogen; Oxygen; Proton exchange membrane fuel cells; Protons; Reduction (metal working); Renewable and Green Energy; Surface stability
• ISSN: 2058-7546; 2058-7546
• DOI: 10.1038/s41560-022-01062-1

Nitrogen-coordinated single atom iron sites (FeN 4 ) embedded in carbon (Fe–N–C) are the most active platinum group metal-free oxygen reduction catalysts for proton-exchange membrane fuel cells. However, current Fe–N–C catalysts lack sufficient long-term durability and are not yet viable for practical applications. Here we report a highly durable and active Fe–N–C catalyst synthesized using heat treatment with ammonia chloride followed by high-temperature deposition of a thin layer of nitrogen-doped carbon on the catalyst surface. We propose that catalyst stability is improved by converting defect-rich pyrrolic N-coordinated FeN 4 sites into highly stable pyridinic N-coordinated FeN 4 sites. The stability enhancement is demonstrated in membrane electrode assemblies using accelerated stress testing and a long-term steady-state test (>300 h at 0.67 V), approaching a typical Pt/C cathode (0.1 mg Pt  cm −2 ). The encouraging stability improvement represents a critical step in developing viable Fe–N–C catalysts to overcome the cost barriers of hydrogen fuel cells for numerous applications. Fe–N–C materials are promising oxygen reduction catalysts for proton-exchange membrane fuel cells but still lack sufficient long-term durability for practical applications. Here the authors fabricate an Fe–N–C material with a thin N–C layer on the surface, leading to a highly durable and active catalyst.