Spatial engineering and d-orbital coupling in axial dual-atom sites for bifunctional oxygen catalysis

Heterogeneous dual-atom catalysts (DACs) offer great potential to enhance electrocatalytic reaction kinetics and provide diverse active sites. However, achieving precise tuning of metal atom coordination in DACs remains a significant challenge. Here, the axial dual atom (ADA) embedded within a covalent organic framework and N-doped graphene, features an axial intermetallic distance tuned by alcohol solvent treatment, resulting in efficient bifunctional electrocatalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In situ X-ray absorption near-edge spectroscopy (XANES) and Raman spectroscopy reveal that Fe acts as the primary active center in the axially coordinated FeCo-ADA, with Co providing synergistic effects. The in-depth theoretical analysis elucidates that the axial Fe-Co orbital coupling results in optimized orbital energy levels, higher Fe oxidation state, weakened oxygen intermediate binding strength, and reduced reaction energy barrier. The zinc-air battery (ZAB) equipped with FeCo-ADA achieves a high peak power density of 464.5 mW cm^-2 and exhibits long rechargeability of 3710 hours at 10 mA cm^-2. Our findings pave an avenue for the rational design in axial DACs to enhance the electrocatalytic performance for energy conversion.