Although recent studies have advanced the understanding of pyrolyzed Fe−N−C materials as oxygen reduction reaction (ORR) catalysts, the atomic and electronic structures of the active sites and their detailed reaction mechanisms still remain unknown. Here, based on first-principles density functional theory (DFT) computations, we discuss the electronic structures of three FeN 4 catalytic centers with different local topologies of the surrounding C atoms with a focus on unraveling the mechanism of their ORR activity in acidic electrolytes. Our study brings back a forgotten, synthesized pyridinic Fe−N coordinate to the community's attention, demonstrating that this catalyst can exhibit excellent activity for promoting direct fourelectron ORR through the addition of a fifth ligand such as −NH 2 , −OH, and −SO 4 . We also identify sites with good stability properties through the combined use of our DFT calculations and Mossbauer spectroscopy data.

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The geometry, electronic structure, and catalytic properties of nitrogen- and phosphorus-doped graphene (N-/P-graphene) are investigated by density functional theory calculations. The reaction between adsorbed O2 and CO molecules on N- and P-graphene is comparably studied via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. The results indicate that a two-step process can occur, namely, CO+O2 →CO2 +Oads and CO+Oads →CO2 . The calculated energy barriers of the first step are 15.8 and 12.4 kcal mol(-1) for N- and P-graphene, respectively. The second step of the oxidation reaction on N-graphene proceeds with an energy barrier of about 4 kcal mol(-1) . It is noteworthy that this reaction step was not observed on P-graphene because of the strong binding of Oads species on the P atoms. Thus, it can be concluded that low-cost N-graphene can be used as a promising green catalyst for low-temperature CO oxidation.

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