Tuning Proton Affinity on Co-N-C Atomic Interface to Disentangle Activity-Selectivity Trade-off in Acidic Oxygen Reduction to HO.

In oxygen reduction reaction to HO via two-electron pathway (2e ORR), adsorption strength of oxygen-containing intermediates determines both catalytic activity and selectivity. However, it also causes activity-selectivity trade-off. Herein, we propose a novel strategy through modulating the interaction between protons and *OOH intermediates to break the activity-selectivity trade-off for highly active and selective 2e ORR. Taking the typical cobalt-nitrogen-carbon single-atom catalyst as an example, boron heteroatoms doped into second coordination sphere of CoN (Co-NBC) increase proton affinity on catalyst surface, facilitating proton attack on the former oxygen of *OOH and thereby promoting HO formation. As a result, Co-NBC simultaneously achieves prominent 2e ORR activity and selectivity in acid with onset potential of 0.724 V vs. RHE and HO selectivity of 94 %, surpassing most reported catalysts. Furthermore, Co-NBC exhibits a remarkable HO productivity of 202.7 mg cm h and a remarkable stability of 60 h at 200 mA cm in flow cell. This work provides new insights into resolving activity-selectivity trade-off in electrocatalysis.