Theoretical Study of the Strain Effect on the Oxygen Reduction Reaction Activity and Stability of FeNC Catalyst
The strain effect on oxygen reduction reaction (ORR) activity and stability of FeNC electrocatalysts has been conducted using the density function theory in this work. Based on the reaction free energy results, the rate-determing step (RDS) of ORR on FeNC is *OH→H2O, when the reaction proceeds with the pathway O2→*OOH→*O→*OH→H2O on Fe site. Tensile stress is favorable to enhance the ORR activity, and the highest ORR activity is obtained on 6%-FeNC electrocatalyst. On the other hand, when the whole oxygen reduction needs the synergy between Fe and adjacent C atoms and proceeds with the pathway O2→*OOH→*TS→*O&#OH→*O→*OH→H2O, the applied stress will decrease the ORR activity of the FeNC electrocatalyst. We further constructed Cu@FeNC core-shell model to simulate strained FeNC. However, adsorption energy of ORR intermediates on Cu@FeNC (1.9%-FeNC) is much weaker than corresponding 2%-FeNC, mainly due to the coordination between the Cu substrate and Fe atom. In addition, the formation energy and binding energy indicate that neither tensile nor compressive stress is conducive to the stability of the FeNC electrocatalyst. In summary, tensile stress could enhance ORR activity of FeNC electrocatalysts when ORR occurs on Fe atom only. What’s more, we should pay more attention to the influence of interface interaction if utilizing M@FeNC model to achieve strained FeNC.