Single Cu–N4 sites enable atomic Fe clusters with high-performance oxygen reduction reactions

Abstract

Atomically dispersed Fe–N₄ catalysts have proven to be promising alternatives to commercial Pt/C for the oxygen reduction reaction. Most reported Fe–N₄ catalysts suffer from inferior O–O bond-breaking capabilities due to superoxo-like O₂ adsorption, though the isolated dual-atomic metal site strategy is extensively adopted. Atomic Fe clusters show greater promise for promoting O–O bond cleavage by undergoing peroxo-like O₂ adsorption. However, the excessively strong binding strength between Fe clusters and oxygenated intermediates sacrifices the activity. Here, we first report a Fe_x/Cu–N@CF catalyst with atomic Fe clusters functionalized by adjacent single Cu–N₄ sites anchored on a porous carbon nanofiber membrane. Theoretical calculation indicates that the single Cu–N₄ sites can modulate the electronic configuration of Fe clusters to reduce the O₂* protonation reaction free energy which ultimately enhances the electrocatalytic performance. In particular, the Cu–N₄ sites can increase the overlap between the d orbitals of Fe and p orbitals of O to accelerate O–O cleavage in OOH*. As a result, this unique atomic catalyst exhibits a half potential (E_1/2) of 0.944 V in alkaline medium, exceeding that of commercial Pt/C, whereas its acidic performance E_1/2 = 0.815 V is comparable to that of Pt/C. This work shows the great potential of single atoms for improvements in atomic cluster catalysts.