Harnessing Pyridinic N Vacancy Defect in Microporous Structures to Induce the Pre-Adsorption of Oxygen and Boost Oxygen Reduction Reaction Kinetics

Defect structures within the carbon matrix play a crucial role in enhancing the oxygen reduction reaction (ORR) activity of Fe single atom and nitrogen-doped catalysts (Fe-N-C SACs). However, overlooking the O₂ pre-adsorption process induced by defective structures hampers the precise identification of active sites and the investigation of the reaction mechanism in Fe-N-C SACs. Hence, we report a Fe SAC with abundant pyridinic N vacancy defects in microporous structures (Fe-N_v-C SAC) and propose a synergistic effect between pyridinic N vacancy defects and O₂ molecules that promotes the kinetics of ORR. The developed Fe-N_v-C SAC demonstrates exceptional ORR performance, exhibiting superior mass activity and turnover frequency compared to conventional Fe-N-C SACs. The in situ Fourier transform infrared spectroscopy (FTIR) and theoretical calculations indicate that pyridinic N vacancy defects in microporous structures facilitate pre-adsorption of O₂ molecules results in the d-band centers of central Fe atoms shifting away from the fermi level. This shift weakens the adsorption strength of *OH species, thereby facilitating the kinetic process of ORR. This work addresses a critical gap in the field of electrocatalysis by providing the experimental validation of pre-adsorption of O₂ molecules on Fe single-atom catalysts, a phenomenon previously only speculated through theoretical calculations.