Mechanism‐Guided Design and Synthesis of Co/Fe Dual‐Sites for Highly Efficient and Selective Oxygen Reduction Reaction

Abstract Overcoming the intrinsic activity‐selectivity contradiction to achieve simultaneously high electrocatalytic activity and near‐unity four‐electron (4e − ) selectivity in the oxygen reduction reaction (ORR) is critical for advancing the efficiency of metal‐air batteries. Transition metal catalysts exhibit divergent ORR behaviors governed by distinct π * d‐orbital occupancies, a phenomenon known as the “oxo‐wall” effect, which dictates the stability of critical terminal metal oxo/oxyl intermediates. The synergistic integration of pre‐ and post‐oxo‐wall metal sites offers a promising strategy to overcome the limitation, while there is a lack of relevant research and understanding of the dual‐site cooperation. Herein, the design and synthesis of a covalently immobilized Co/Fe‐porphyrin catalyst are reported to validate a dual‐site cascade mechanism: O 2 undergoes initial two‐electron (2e − ) reduction at post‐oxo‐wall Co sites exhibiting high activity but low 4e − selectivity, followed by sequential H 2 O 2 reduction to H 2 O at pre‐oxo‐wall Fe sites with high 4e − selectivity. Spatial isolation enforced by porphyrin ligands and covalent grafting prevents inter‐sites interference. This architecture successfully circumvents the activity‐selectivity contradiction, delivering enhanced ORR performance with a half‐wave potential of 0.79 V vs RHE alongside high 4e − selectivity. The work provides molecular‐level insights into decoupling activity‐selectivity trade‐offs, establishing a dual‐site design paradigm for energy conversion electrocatalysts.