Harnessing geometric distortion to stimulate oxygen reduction activity of atomically dispersed Fe catalysts in...

To achieve precise optimization of the geometric structure and control over spatial distribution of single atom active sites, we introduce an in situ polymer layer modification strategy. Through co-deposition of tannic acid (TA) and polyethyleneimine (PEI) on carbon nanotubes (CNTs), the polymer improves the dispersion and prevents the agglomeration of Fe atoms. Consequently, after controlled calcination, the geometrically distorted Fe-N₄ single atom active sites are constructed on the surface of the curved carbon support. The optimized distortion reduces the reaction energy barrier, optimizes the adsorption energy of oxygen intermediates, and leading to a remarkable improvement of oxygen reduction reaction (ORR) activity. As the result, the obtained single atom catalyst (SAC) Fe-NC@CNTs exhibits exceptional performance with a large onset potential (E_onset) of 1.03 V and a half-wave potential (E_1/2) of 0.91 V in 0.1 M KOH solution, surpassing the previously reported ORR electrocatalysts. Benefitting from these features, Fe-NC@CNTs-based rechargeable aqueous Zn-air battery (A-ZAB) delivers a higher power density of 209.5 mW cm^-2 and can sustain stable changing/discharging for over 2000 h and experiences negligible charge-discharge potential gap fluctuation, being the most booming competitor among the reported electrocatalysts. Furthermore, quasi-solid-state Zn-air battery (QSS-ZAB) with Fe-NC@CNTs air cathode exhibits an impressive peak power density of 130.8 mW cm^-2, large round-trip efficiency of 82 %, and long cycling life of over 100 h. Our work reveals the relationship of strain-induced geometrical distortion and the structure activity relationship, offering a new way for the rational design of other highly efficient catalytic systems.