Investigation on the demetallation of Fe-N-C for oxygen reduction reaction: The influence of structure and structural evolution of active site.

Iron-nitrogen-carbon (Fe-N-C) catalysts for oxygen reduction reaction (ORR) are promising candidates in fuel cell devices but the poor stability remains a grave challenge. The elimination of demetallation is pivotal for extending the life but still incapable due to the ambiguous mechanism. Herein, we show that the structure of FeN 4 site and its structural evolution during ORR has the significant influence. The end-of-test/in-situ Mössbauer spectroscopy and density functional theory study reveal that D1 mainly contributes to the ORR activity but suffers severe demetallation, which is likely due to the instability of FeN 4 C 8. The faster demetallation during ORR, especially at higher potential, can be attributed to the weaker coordination of FeN 4 induced by oxygenated intermediate and electric field according to ab initio molecular dynamics simulations. Finally, the binding energy of Fe-N bond is introduced to describe the influence of structure and structural evolution and give guidance to the improvement of stability. The influence of structure and structural evolution of active site on the demetallation of Fe-N-C is investigated by the end-of-test/in-situ Mössbauer spectroscopy and ab initio molecular dynamics simulation. [Display omitted] • The demetallation related to the degradation of Fe-N-C for ORR is studied. • The stability and activity of FeN 4 varied by structure are identified. • The effect of structural evolution of FeN 4 on demetallation is determined. • The stability and activity mapping of various active sites is exhibited. [ABSTRACT FROM AUTHOR]