Simultaneously breaking the axial and planar symmetry further boosts the oxygen electroreduction activities of Fe-N4 sites

Breaking the geometric symmetry of the electron distribution is a promising way to improve the oxygen reduction reaction (ORR) activity of the Fe-N 4 sites, which was typically achieved by introducing heteroatoms horizontally or vertically. In this work, we developed a strategy to simultaneously break the axial and planar symmetry of Fe-N 4 sites for the first time by engaging axial chlorine and planar defects. This strategy not only destroys the symmetrical electron distribution of the Fe-N 4 site but also enables a larger orbital overlap between Cl-3p and Fe-3d, which accelerates the *OH desorption and reduces the overpotential. The resulting Fe-N 4 Cl (A) catalyst exhibited the half-wave potential as high as 0.91 V. In-situ X-ray absorption spectra revealed that it effectively suppressed Fe dissolution during the ORR process and achieved high catalytic stability. Benefiting from the free-standing nature of blow-spun fibers, the Fe-N 4 Cl (A) catalyst membrane can be directly used as the air cathode of the solid-state zinc-air batteries (ZABs), avoiding the use of inactive binders that hinder conductivity/air transportation, and preventing the catalyst from peeling off, thereby showing excellent performance in solid-state ZABs. This work provides fundamental insights for developing high-performing cathode materials for solid-state ZABs via surface engineering strategies.