F-axial-coordinated Fe single atoms confined in a honeycombed nitrogen-doped carbon framework for efficient oxygen reduction reaction

Axial coordination of heteroatoms to the metal sites in M-N-C catalysts exerts a direct modulation of the electronic distribution by forming a bond with the metal center, thereby optimizing its intrinsic oxygen reduction reaction (ORR). However, the steric hindrance introduced by axially coordinated heteroatoms limits reactant accessibility, potentially suppressing the overall catalytic activity. This study provides an HF wet etching strategy to synthesize a hollow porous ZIF-derived nitrogen-doped carbon-supported F-axially coordinated single-atom iron catalyst (F-Fe 1 @HNC), which simultaneously achieves F-axial coordination and high reactant accessibility. Consequently, the F-Fe 1 @HNC catalyst demonstrates outstanding ORR performance in both alkaline (0.919 V) and acidic (0.797 V) electrolytes. When employed as a cathode material in a zinc-air battery, F-Fe 1 @HNC achieves an open-circuit potential of 1.477 V and a power density of 256 mW cm −2 , significantly outperforming commercial Pt/C catalysts. Density functional theory confirmed that F-coordination altered the electronic distribution at Fe-N-C sites, optimizing the adsorption of oxygen-containing intermediates. This work highlights the importance of electron-withdrawing groups in creating the electron asymmetry at Fe-N-C sites, providing profound insights into designing highly efficient ORR catalysts. The F-axis coordinated Fe-N-C catalyst breaks the limitation imposed by spatial steric hindrance and significantly improves the oxygen reduction reaction (ORR) performance. Download: Download high-res image (252KB) Download: Download full-size image