Boron in the Second Coordination Sphere of Fe Single Atom Boosts the Oxygen Reduction Reaction.

Metal single atoms coordinated with four nitrogen atoms (MN) are regarded as tremendously promising catalysts for the electrocatalytic oxygen reduction reaction (ORR). Nevertheless, the strong bond intensity between the metal center and the O atom in oxygen-containing intermediates significantly limits the ORR activity of MN. Herein, the catalytically active B atom is successfully introduced into the second coordination sphere of the Fe single atom (FeN-B-C) to realize the alternative binding of B and O atoms and thus facilitate the ORR activity. Compared with the pristine FeN catalyst, the synthesized FeN-B-C catalyst exhibits improved ORR catalytic capability with a half-wave potential () of 0.80 V and a kinetic current density () of 5.32 mA cm in acid electrolyte. Moreover, in an alkaline electrolyte, the FeN-B-C catalyst displays remarkable ORR activity with of 0.87 V and of 8.94 mA cm at 0.85 V, outperforming commercial Pt/C. Notably, the mechanistic study has revealed that the active center is the B atom in the second coordination shell of the FeN-B-C catalyst, which avoids the direct bonding of Fe-O. The B center has a moderate binding force to the ORR intermediate, which flattens the ORR energy diagram and thereby improves the ORR performance. Therefore, this study offers a novel strategy for tailoring catalytic performance by tuning the active center of single-atom catalyst.