Thermally Driven Structure and Performance Evolution of Atomically Dispersed FeN4 Sites for Oxygen Reduction

• Published in: Angewandte Chemie (International ed.) 2019-12, Vol.58 (52), p.18971-18980
• Main Authors: Li, Jiazhan, Zhang, Hanguang, Samarakoon, Widitha, Shan, Weitao, Cullen, David A., Karakalos, Stavros, Chen, Mengjie, Gu, Daming, More, Karren L., Wang, Guofeng, Feng, Zhenxing, Wang, Zhenbo, Wu, Gang
• Format: Article
• Language: English
• Subjects: Activation; atomically dispersed active site; Bonding; Carbon; Carbonization; Chemical reduction; Doping; electrode materials; formation mechanism; Fuel technology; Graphitization; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Iron; nanomaterials; Nitrogen; Oxygen; oxygen reduction reaction; Oxygen reduction reactions; Platinum; Porosity; proton exchange membrane fuel cell; Proton exchange membrane fuel cells; Temperature
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201909312

FeN4 moieties embedded in partially graphitized carbon are the most efficient platinum group metal free active sites for the oxygen reduction reaction in acidic proton‐exchange membrane fuel cells. However, their formation mechanisms have remained elusive for decades because the Fe−N bond formation process always convolutes with uncontrolled carbonization and nitrogen doping during high‐temperature treatment. Here, we elucidate the FeN4 site formation mechanisms through hosting Fe ions into a nitrogen‐doped carbon followed by a controlled thermal activation. Among the studied hosts, the ZIF‐8‐derived nitrogen‐doped carbon is an ideal model with well‐defined nitrogen doping and porosity. This approach is able to deconvolute Fe−N bond formation from complex carbonization and nitrogen doping, which correlates Fe−N bond properties with the activity and stability of FeN4 sites as a function of the thermal activation temperature. FeN4 moieties embedded in partially graphitized carbon are efficient active sites for the oxygen reduction reaction in acidic proton‐exchange membrane fuel cells. The mechanisms leading to the formation of these active sites were studied by introducing Fe ions into a nitrogen‐doped carbon followed by controlled thermal activation.