Product selectivity in multielectron electrocatalytic reactions is crucial to energy conversion efficiency and chemical production. However, a present practical drawback is the limited understanding of actual catalytic active sites. Here, using as a prototype single-atom catalysts (SACs) in acidic oxygen reduction reaction (ORR), we report the structure–property relationship of catalysts and show for the first time that molecular-level local structure, including first and second coordination spheres (CSs), rather than individual active atoms, synergistically determines the electrocatalytic response. ORR selectivity on Co-SACs can be tailored from a four-electron to a two-electron pathway by modifying first (N or/and O coordination) and second (C–O–C groups) CSs. Using combined theoretical predictions and experiments, including X-ray absorption fine structure analyses and in situ infrared spectroscopy, we confirm that the unique selectivity change originates from the structure-dependent shift of active sites from the center Co atom to the O-adjacent C atom. We show this optimizes the electronic structure and *OOH adsorption behavior on active sites to give the present “best” activity and selectivity of >95% for acidic H2O2 electrosynthesis.

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Demonstrated here is the correlation between atomic configuration induced electronic density of single‐atom Co active sites and oxygen reduction reaction (ORR) performance by combining density‐functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, a MOF‐derived Co single‐atom catalyst with the optimal Co1‐N3PS active moiety incorporated in a hollow carbon polyhedron (Co1‐N3PS/HC) was designed and synthesized. Co1‐N3PS/HC exhibits outstanding alkaline ORR activity with a half‐wave potential of 0.920 V and superior ORR kinetics with record‐level kinetic current density and an ultralow Tafel slope of 31 mV dec−1, exceeding that of Pt/C and almost all non‐precious ORR electrocatalysts. In acidic media the ORR kinetics of Co1‐N3PS/HC still surpasses that of Pt/C. This work offers atomic‐level insight into the relationship between electronic density of the active site and catalytic properties, promoting rational design of efficient catalysts.