Computational Modelling of Pyrrolic MN 4 Motifs Embedded in Graphene for Catalyst Design.

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]