TY - JOUR
T1 - Evolution Pathway from Iron Compounds to Fe1(II)-N4 Sites through Gas-Phase Iron during Pyrolysis
AU - Li, Jingkun
AU - Jiao, Li
AU - Wegener, Evan
AU - Richard, Lynne Larochelle
AU - Liu, Ershuai
AU - Zitolo, Andrea
AU - Sougrati, Moulay Tahar
AU - Mukerjee, Sanjeev
AU - Zhao, Zipeng
AU - Huang, Yu
AU - Yang, Fan
AU - Zhong, Sichen
AU - Xu, Hui
AU - Kropf, A. Jeremy
AU - Jaouen, Frédéric
AU - Myers, Deborah J.
AU - Jia, Qingying
N1 - Publisher Copyright:
© 2019 American Chemical Society.
PY - 2020/1/22
Y1 - 2020/1/22
N2 - Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap obscures the connections between the input precursors and the output products, clouding the pathway toward Fe-N-C catalyst improvement. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single-atom Fe1(II)-N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that diffuses into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor-phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via "noncontact pyrolysis" wherein the Fe precursor is not in physical contact with the N and C precursors during pyrolysis.
AB - Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap obscures the connections between the input precursors and the output products, clouding the pathway toward Fe-N-C catalyst improvement. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single-atom Fe1(II)-N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that diffuses into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor-phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via "noncontact pyrolysis" wherein the Fe precursor is not in physical contact with the N and C precursors during pyrolysis.
UR - http://www.scopus.com/inward/record.url?scp=85078335253&partnerID=8YFLogxK
U2 - 10.1021/jacs.9b11197
DO - 10.1021/jacs.9b11197
M3 - Article
C2 - 31880925
AN - SCOPUS:85078335253
SN - 0002-7863
VL - 142
SP - 1417
EP - 1423
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 3
ER -