LAUSR

Electrocatalytic oxidation of organics using water as the oxygen source is a prospective but challenging method to produce high‐value‐added chemicals; especially, the competitive oxygen evolution reaction (OER) limits its efficiency. Herein, a tandem catalysis strategy based on a single‐atom catalyst with Cr atoms atomically dispersed at a CoSe2 support (Cr1/CoSe2) is presented. Thereinto, Co and Cr sites are endowed with a specific function to activate water and styrene respectively, and the competition between the OER and styrene oxidation is turned into mutual benefits via cooperated active sites. Under a potential of 1.6 VAg/AgCl, excellent selectivity of 95% to benzaldehyde and a high conversion rate of styrene at 88% without any exogenous oxidizing reagent are achieved. Isotopic tracing, isotope‐labeled in situ Raman spectra, and detailed theoretical calculation further reveal the tandem mechanism, showing that the transfer of *OOH intermediates from the Co to the Cr sites serves as a bridge to link the oxidation of water and styrene. This work develops a new strategy for the co‐oxidation of multi‐species based on tandem catalysis, providing novel insights for the design of single‐atom catalysts.