Influence of metal precursor in the structure and electrocatalytic response of Fe,Co-N/C single atom catalysts synthesized by Laser pyrolysis: a XANES and EXAFS study

In the last decade Single-Atom Catalysts (SACs) have become the new frontier in heterogeneous catalysis. Because of their atomic dispersion, SACs ideally represent the utmost
utilization of metals, where every atom is, in principle, able to participate in the catalytic reaction. Moreover, the support anchoring the SACs plays a role in tuning their activity and selectivity, not unlike the ligands in homogeneous organometallic catalysis. For these reasons SACs has been invoked as the link able to bridge homogeneous and heterogeneous catalysts, leveraging the best features of both worlds. So far, SACs have offered promising results in a variety of fields, including energy, environmental and biomedical applications. However, achieving the full potential of SACs will require not only a rational design based on a better theoretical understanding of the SAC support interaction, but especially, a new generation of synthesis methods capable of delivering the required catalytic structures.
Stabilizing atomically dispersed metal atoms (or even low-number clusters) remains a formidable synthesis challenge due to the high surface energy of single atoms. Current synthesis methods to obtain SACs include high temperature treatments of organic precursors such as Metallic Organic Frameworks, photochemically induced reductions under refrigeration or the atomic layer deposition of organometallic precursors. These protocols often involve multiple steps, post-treatments and the use of additives to minimize aggregation, increasing cost, lowering reproducibility and hampering the scaling-up.
We have developed the laser-driven pyrolysis of aerosolized precursors into a powerful technique able to produce homogeneous M-N@C SACs (M = Fe, Co) with high metal loading. The generated SACs will be exploited in electrochemical reactions for green-energy production, such as, oxygen reaction reduction. XANES and EXAFS at the K-edge of the non-noble catalyst, single atom of Fe is necessary to fully characterize Fe-N@C samples, determining Fe-neighbour distances, chemical state and aggregation depending on Fe % in weight.