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: O2 undergoes initial two-electron (2e−) reduction at post-oxo-wall Co sites exhibiting high activity but low 4e− selectivity, followed by sequential H2O2 reduction to H2O 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.
DOI://doi.org/10.1002/adfm.202523551
