Regulating d‐Orbital Hybridization of Subgroup‐IVB Single Atoms for Efficient Oxygen Reduction Reaction

Abstract Highly active single‐atom electrocatalysts for the oxygen reduction reaction are crucial for improving the energy conversion efficiency, but they suffer from a limited choice of metal centers and unsatisfactory stabilities. Here, this work reports that optimization of the binding energies for reaction intermediates by tuning the d ‐orbital hybridization with axial groups converts inactive subgroup‐IVB (Ti, Zr, Hf) moieties (MN 4 ) into active motifs (MN 4 O), as confirmed with theoretical calculations. The competition between metal‐ligand covalency and metal‐intermediate covalency affects the d‐p orbital hybridization between the metal site and the intermediates, converting the metal centers into active sites. Subsequently, dispersed single‐atom M sites coordinated by nitrogen/oxygen groups have been prepared on graphene (s‐M‐N/O‐C) catalysts on a large‐scale with high‐energy milling and pyrolysis. Impressively, the s‐Hf‐N/O‐C catalyst with 5.08 wt% Hf exhibits a half‐wave potential of 0.920 V and encouraging performance in a zinc‐air battery with an extraordinary cycling life of over 1600 h and a large peak power‐density of 256.9 mW cm −2 . This work provides promising single‐atom electrocatalysts and principles for preparing other catalysts for the oxygen reduction reaction.