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. Tuning of metal atom coordination in dual atom catalysts remains challenging. Here, axial dual Fe-Co atoms are incorporated into a COF and N-doped graphene, as bifunctional oxygen catalyst. The axial Fe-Co orbital coupling optimizes orbital energy levels enhancing its electrocatalytic performance.