Sublimation Transformation Synthesis of Dual-Atom Fe Catalysts for Efficient Oxygen Reduction Reaction

Dual-atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual-atom Fe catalysts (Fe₂/NC) by utilizing in situ generated Fe₂Cl₆(g) dimers from FeCl₃(s). The structure of Fe₂/NC was investigated by aberration-corrected transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy. As-obtained Fe₂/NC, with a Fe-Fe distance of 0.3 nm inherited from Fe₂Cl₆, displayed superior oxygen reduction performance with a half-wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single-atom catalyst (Fe₁/NC), and its counterpart with a common and shorter Fe-Fe distance of ~0.25 nm (Fe₂/NC-S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe-Fe distance in Fe₂/NC is crucial for the O₂ adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual-site catalysis.