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![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
Published on: December 4, 2017
Evolution Pathway from Iron Compounds to Fe1(II)-N4 Sites through Gas-Phase Iron during Pyrolysis
Jingkun Li1, Li Jiao, Evan Wegener2
1Institut Charles Gerhardt Montpellier, UMR 5253, CNRS , Université Montpellier, ENSCM , Place Eugène Bataillon , 34095 Montpellier cedex 5 , France.
Abstract:
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.
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