Combining the abundance and inexpensiveness of their constituent elements with their atomic dispersion, atomically dispersed Fe–N–C catalysts represent the most promising alternative to precious-metal-based materials in proton exchange membrane (PEM) fuel cells. Due to the high temperatures involved in their synthesis and the sensitivity of Fe ions toward carbothermal reduction, current synthetic methods are intrinsically limited in type and amount of the desired, catalytically active Fe–N₄ sites, and high active site densities have been out of reach (dilemma of Fe–N–C catalysts). We herein identify a paradigm change in the synthesis of Fe–N–C catalysts arising from the developments of other M–N–C single-atom catalysts. Supported by DFT calculations we propose fundamental principles for the synthesis of M–N–C materials. We further exploit the proposed principles in a novel synthetic strategy to surpass the dilemma of Fe–N–C catalysts. The selective formation of tetrapyrrolic Zn–N₄ sites in a tailor-made Zn–N–C material is utilized as an active-site imprint for the preparation of a corresponding Fe–N–C catalyst. By successive low- and high-temperature ion exchange reactions, we obtain a phase-pure Fe–N–C catalyst, with a high loading of atomically dispersed Fe (>3 wt %). Moreover, the catalyst is entirely composed of tetrapyrrolic Fe–N₄ sites. The density of tetrapyrrolic Fe–N₄ sites is more than six times as high as for previously reported tetrapyrrolic single-site Fe–N–C fuel cell catalysts.

Metal- and nitrogen-doped carbon materials (M–N–Cs) have emerged as promising alternatives to costly platinum-group metals (PGMs) for the oxygen reduction reaction (ORR) in renewable energy applications. Notably, there is increasing experimental and theoretical evidence supporting pyrrolic MN₄ coordination over pyridinic MN₄ in these materials, which aligns closer to the MN₄ geometries found in nature. This study utilizes density functional theory (DFT) to elucidate the ability of each metal to catalyze various ORR mechanisms at the pyrrolic MN₄ sites. Among the M–N–Cs of first–row transition metals, pyrrolic CrN₄ and FeN₄ exhibit exceptional 4e-ORR activity, promoting both inner- and outer-sphere mechanisms and H₂O₂ dissociation. Pyrrolic CoN₄ is also promising for 2e-ORR catalysis due to its effective outer-sphere electron-transfer capabilities. These findings offer valuable insights for designing sustainable electrocatalysts to exploit the full potential of renewable energy sources, advancing the path toward carbon neutrality.

Catalysts are required to ensure electrochemical reduction of CO₂ to fuels proceeds at industrially acceptable rates and yields. As such, highly active and selective catalysts must be developed. Herein, a density functional theory study of p‐block element and noble metal doped graphene‐based single‐atom catalysts in two defect sites for the electrochemical reduction of CO₂ to CO and HCOOH is systematically undertaken. It is found that on all of the systems considered, the thermodynamic product is HCOOH. Pb/C₃, Pb/N₄ and Sn/C₃ are identified as having the lowest overpotential for HCOOH production while Al/C₃, Al/N₄, Au/C₃ and Ga/C₃ are identified as having the potential to form higher order products due to the strength of binding of adsorbed HCOOH.

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 $\pi$-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 $\pi$-system.

Methanol oxidation on the stepped Au(332) surface was investigated by pulsed isothermal molecular beam (MB) experiments. The effect of the surface temperature as well as the influence of changes in the methanol and atomic oxygen flux on the partial oxidation to methyl formate was studied. A maximum in methyl formate formation is observed at 250 K under the applied single collision conditions. Increasing the methanol to oxygen ratio was found to increase the selectivity to methyl formate and decrease unwanted overoxidation to surface deactivating formate detected by in situ infrared reflection absorption spectroscopy (IRAS). The results show evidence for the importance of an additional deactivation mechanism for methyl formate formation connected to methanol which is active under oxygen-deficient conditions at low temperatures. Moreover, the measurements suggest a small number of sites to be highly reactive for methyl formate formation which are preferentially blocked under oxygen-deficient conditions.

A promising alternative for platinum-based electrocatalysts for the oxygen reduction reaction are single-atom catalysts, particularly those based on iron, nitrogen and carbon. The active sites in these FeNC catalysts are conceived of as individual FeN₄ centres embedded in a carbon matrix, often approximated by a planar sheet. While the coordination of FeN₄ centres via pyridinic nitrogen atoms, i.e. six-membered rings, does not break the symmetry of the graphene plane, coordination via pyrrolic, i.e. five-membered rings, induces defects in the carbon matrix that can lift its planarity. Deviation from planarity is expected to influence the electronic properties of the FeN₄ centres. An open question is whether spectroscopic techniques can detect such differences. Among these, Mössbauer spectroscopy is of central importance to characterising FeNC catalyst materials. Since pyrrolic models have recently emerged as a spectroscopically and thermodynamically consistent model for FeNC active sites, we herein compare three different pyrrolic FeN₄ models proposed in the literature and discuss whether and how these pyrrolic centres can be discerned spectroscopically.