Regulating the Coordination Geometry and Oxidation State of Single‐Atom Fe Sites for Enhanced Oxygen Reduction Electrocatalysis

Abstract

FeNC catalysts demonstrate remarkable activity and stability for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells and Zn–air batteries (ZABs). The local coordination of Fe single atoms in FeNC catalysts strongly impacts ORR activity. Herein, FeNC catalysts containing Fe single atoms sites with FeN3, FeN4, and FeN5 coordinations are synthesized by carbonization of Fe‐rich polypyrrole precursors. The FeN5 sites possess a higher Fe oxidation state (+2.62) than the FeN3 (+2.23) and FeN4 (+2.47) sites, and higher ORR activity. Density functional theory calculations verify that the FeN5 coordination optimizes the adsorption and desorption of ORR intermediates, dramatically lowering the energy barrier for OH− desorption in the rate‐limiting ORR step. A primary ZAB constructed using the FeNC catalyst with FeN5 sites demonstrates state‐of‐the‐art performance (an open circuit potential of 1.629 V, power density of 159 mW cm−2). Results confirm an intimate structure‐activity relationship between Fe coordination, Fe oxidation state, and ORR activity in FeNC catalysts.

Converting carbon black into an efficient and multi-site ORR electrocatalyst: the importance of bottom-up construction parameters

“…The results herein reported were compared to those published in the 10 latest publications on the application of carbon materials enriched with Fe-N-C active sites for the ORR in basic media (Table S12 †). [31][32][33][34][35][36][37][38][39][40] The very different experimental conditions employed render difficult a fair comparison. In fact, this is a common issue that might negatively affect developments in ORR electrocatalysts.…”

Recent progress in high-loading single-atom catalysts and their applications

“…In conclusion, high-loading SACs are now being widely used in photocatalysis, electrocatalysis and thermal catalysis. 92,93 It's important to note that while high-loading SACs can offer advantages in these applications, there may still be challenges to overcome, such as stability under harsh reaction conditions or the requirement for specific support materials. Further research and development efforts are ongoing to optimize the design, synthesis, and utilization of high-loading SACs in different catalytic reactions.…”

Optimizing reaction intermediate adsorption by engineering the coordination structure of single-atom Fe–N5–C electrocatalysts for efficient oxygen reduction

“…[30][31][32] In addition, several recent works have verified that the change of the coordination structure can have a positive effect on the ORR process. 20,33,34 Nevertheless, it is still a great challenge to deeply understand the correlation between the coordination structure and intermediate adsorption on catalysts for the ORR from the perspective of the adsorption energy of intermediates.…”