Insights into the enhanced ORR activity of FeN4-embedded graphene through interface interactions with metal substrates: Electronic vs. geometric descriptors

Abstract

Recent experiments have revealed that the oxygen reduction reaction (ORR) performances of transition-metal and nitrogen codoped carbon (TM-N-C) can be drastically improved by interfacing with TM nanoparticles. However, the key factors that derive from this emerging composite SAC and can well correlate with the boosted ORR activity is still unclear. Herein, taking the FeN₄-embedded graphene (FeN₄-G) as example, we built a series of model heterointerface systems, by placing FeN₄-G on various common TM surfaces (denoted as FeN₄-M), to explore the enhancement origin. Based on extensive density functional theory calculations, we find that all the FeN₄-M systems exhibit higher ORR activity than the free-standing FeN₄-G, and even most FeN₄-M systems are much more active than the Pt(111) surface. Furthermore, for the descriptor construction, however there is no apparent correlation between the ORR activity and the electronic structures of Fe active centers, the ones that are closely relevant with ORR activity of the free-standing FeN₄-G. Instead, interestingly the interlayer distance between FeN₄-G and the underlying metal substrates, an intrinsic geometric structure parameter, has been identified to linearly correlate with the binding strengths of ORR intermediates and ORR overpotential well. Present work provides a novel insight into the structure-activity relationship of the composite SACs consisting of Fe-N-C and metal nanoparticles.