Ammonia capture by MN4 (M = Fe and Ni) clusters embedded in graphene

Computational Modelling of Pyrrolic MN4 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. MN4 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 MN4 motifs, recent studies have elucidated the role of tetrapyrrolic MN4 motifs in electrocatalysis. Using density functional theory, we constructed and compared various structural models to study the incorporation of tetrapyrrolic and tetrapyridinic MN4 motifs in 2D carbon materials and analyzed the type of interactions between each metal species and the N4 site. We further quantified the relative affinity of various metal species to the two types of N4 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 MN4 motifs compared to species that participate in covalent interactions with the π-system. Furthermore, the binding strength of each species in the N4 site depend on the electronegativity as well as the availability of orbitals for accepting electrons from the π-system.

Metal-Nitrogen-Carbon Catalysts of Specifically Coordinated Configurations toward Typical Electrochemical Redox Reactions

Metal-nitrogen-carbon (M-N-C) material with specifically coordinated configurations is a promising alternative to costly Pt-based catalysts. In the past few years, great progress is made in the studies of M-N-C materials, including the structure modulation and local coordination environment identification via advanced synthetic strategies and characterization techniques, which boost the electrocatalytic performances and deepen the understanding of the underlying fundamentals. In this review, the most recent advances of M-N-C catalysts with specifically coordinated configurations of M-N_x (x = 1-6) are summarized as comprehensively as possible, with an emphasis on the synthetic strategy, characterization techniques, and applications in typical electrocatalytic reactions of the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, CO₂ reduction reaction, etc., along with mechanistic exploration by experiments and theoretical calculations. Furthermore, the challenges and potential perspectives for the future development of M-N-C catalysts are discussed.