Role of Local Carbon Structure Surrounding FeN₄ Sites in Boosting the Catalytic Activity for Oxygen Reduction

Development of effective nonprecious metal and nitrogen codoped carbon catalysts for the oxygen reduction reaction (ORR) requires a fundamental understanding of the mechanisms underlying their catalytic activity. In this study, we employed the first-principles density functional theory calculations to predict some key parameters (such as activation energy for O-O bond breaking and free-energy evolution as a function of electrode potential) of ORR on three FeN₄-type active sites with different local carbon structures. We find that the FeN₄ site surrounded by eight carbon atoms and at the edge of micropores has the lowest activation energy (about 0.20 eV) for O-O bond breaking among the three FeN₄-type active sites for promoting a direct four-electron ORR. Consequently, our computational results suggest that introduction of micropores in the nonprecious metal catalysts could enhance their catalytic activity for ORR through facilitating the formation of FeN₄-C₈ active sites with high specific activity.