Atomic defects engineering on Fe-N₄ sites for boosting oxygen reduction by in-situ ZnO thermal etching strategy

Designing atomic defects engineering is significant for boosting the activity of metal catalytic sites. Herein, we constructed Fe-N₄ sites on defective N-doped carbon catalyst (Fe-N₄/def-CN) by in-situ ZnO thermal etching strategy. Compared with defect-free Fe-N₄/CN, Fe-N₄/def-CN had a half-wave potential (E_1/2) of 0.920 V vs RHE for alkaline ORR with 50 mV increasing. We directly observed the ZnO in-situ disappearance, studied ZnO thermal etching effect on CN substrate and revealed the mechanism of carbon defect formation by in-situ environmental transmission electron microscopy (ETEM) and in-situ X-ray diffraction (XRD) measurements. Density functional theory (DFT) calculations demonstrated the easier formation of double carbon-atoms defects adjacent to Fe-N₄ sites. The carbon-atoms defects and Zn-atom vacancies synergistically improved the ORR activity of Fe-N₄ sites. This work provides a atomic-level insight to optimize the atomic defects engineering of metal-N₄ sites, such as carbon-atoms defects and metal-atoms vacancies by in-situ ZnO thermal etching strategy.