Alkali Metal Cation-Regulated Interfacial Electric Fields Enable Selective C─H Oxidation via Reactive Oxygen Species.

Precise control over C─H oxidation remains challenging due to the intrinsic coupling between the generation and reactivity of oxygen-based oxidants. Here, we identify the interfacial electric field as an effective reaction coordinate that decouples these processes, enabling selective pathways inaccessible under conventional thermodynamic control. To realize this concept, a defect-rich carbon catalyst is employed to generate surface-bound *OOH species via the two-electron oxygen reduction reaction. By varying electrolyte cations, the interfacial electric field is systematically modulated, which in turn modulates the spatiotemporal distribution and reactivity of reactive oxygen species. Using butanone oxidation as a model reaction, we find that Na+ selectively promotes α-hydroxylation, whereas Li+ favors deeper dehydrogenation pathways. These findings establish the interfacial electric field as a tunable parameter for controlling reaction selectivity and provide a general strategy for decoupling oxidant generation from reactivity in electrocatalytic transformations.