Effect of Fe–N–C single atom/cluster catalyst on ORR of PEMFC

With the continuous advancement of fuel cell technology, the exploration and development of highly efficient non - precious - metal catalysts for the oxygen reduction reaction (ORR) have emerged as a focal point of research. Fe–N–C catalysts have attracted much attention due to their excellent performance and low cost, and coupling single-atom catalysts (SACs) with atomic clusters (ACs) is an effective method to improve catalyst activity. This study used the pyrolysis method to synthesize iron atom catalysts (Fe–N–C SACs) and iron cluster coupled catalysts (Fe–N–C SACs/ACs) on ZIF-8 carbon support. It evaluated the catalyst performance through electrochemical testing. The experimental results showed that the introduction of Fe clusters improved the half-wave potential of the catalyst to 0.399 V, which represented an 8.2 % enhancement compared to the SAC catalyst and reached 87.1 % of that of the commercial Pt–C catalyst, and reduced the Tafel slope to 61.47 mV dec −1 , effectively improving the ORR activity of the catalyst. We constructed FeN 4 single atom catalyst models and FeN 4 /Fe 4 N 6 single atom cluster catalyst models using density functional theory (DFT), analyzed their electronic structures and reaction mechanisms, and revealed the mechanism of action of iron clusters. DFT calculations showed that iron clusters altered the charge distribution of FeN 4 sites, reducing the rate determining step (RDS) (OH desorption) energy to 0.5 eV, which promoted the desorption of products and the re-adsorption of reactants. As a result, the superior electrocatalytic performance of Fe–N–C SAC/AC is attributed to the synergistic effect between iron clusters and single atoms, which is influenced by the coordination environment and provides new ideas for designing efficient ORR catalysts.