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Development and fundamental understanding of precious‐group‐metal‐free electrocatalysts is hampered by limitations in the quantification of the intrinsic activity of different catalytic sites and understanding the different reaction mechanisms. Comparing isomorphic nitrogen‐doped carbons, Zn‐N‐Cs and Fe‐N‐Cs with the common tetrapyrrolic motif, a catalyst‐independent outer‐sphere rate‐determining step in the alkaline oxygen reduction reaction is observed. Density functional theory (DFT) simulations on tetrapyrrolic model structures indicate the highest occupied molecular orbital (HOMO) level as a good descriptor for the catalytic activity. Contour plots suggest that the electron transfer occurs directly from the tetrapyrrolic coordination site, rather than from the metal center. Metal‐free tetrapyrrolic N4 sites are discovered to be highly active oxygen reduction reaction (ORR) active sites in alkaline that reach turnover frequencies (TOF) of 0.33 and 1.84 s−1 at 0.80  and 0.75 VRHE in the order of magnitude of tetrapyrrolic Fe–N4 sites in the acidic ORR. While Zn‐coordination lowers the HOMO level and therefore the catalytic activity, Fe‐coordination lifts the HOMO level resulting in TOF values of 0.4  and 4 s−1 for tetrapyrrolic Fe–N4 sites at 0.90  and 0.85 VRHE, respectively. At higher mass activities, the peroxide reduction becomes rate‐limiting, where highest peroxide production rates are observed for the nitrogen‐doped carbon. [ABSTRACT FROM AUTHOR]

Carbon-based materials doped with metal and nitrogen (M-N-Cs) have promising potential in electrocatalytic applications with the advantage of material sustainability. MN 4 motifs incorporated into a carbon lattice are generally known to be responsible for the activity of these materials. While many computational studies assume the tetrapyridinic MN 4 motifs, recent studies have elucidated the role of tetrapyrrolic MN 4 motifs in electrocatalysis. Using density functional theory, we constructed and compared various structural models to study the incorporation of tetrapyrrolic and tetrapyridinic MN 4 motifs in 2D carbon materials and analyzed the type of interactions between each metal species and the N 4 site. We further quantified the relative affinity of various metal species to the two types of N 4 site. Upon analysis of energies, bond lengths, electronic population and charges, we found that metals that exhibit highly ionic binding characters have a greater affinity towards tetrapyrrolic MN 4 motifs compared to species that participate in covalent interactions with the π -system. Furthermore, the binding strength of each species in the N 4 site depend on the electronegativity as well as the availability of orbitals for accepting electrons from the π -system. [ABSTRACT FROM AUTHOR]