AbstractElucidating the synergistic catalytic mechanism between multiple active centers is of great significance for heterogeneous catalysis; however, finding the corresponding experimental evidence remains challenging owing to the complexity of catalyst structures and interface environment. Here we construct an asymmetric TeN₂–CuN₃ double-atomic site catalyst, which is analyzed via full-range synchrotron pair distribution function. In electrochemical CO₂ reduction, the catalyst features a synergistic mechanism with the double-atomic site activating two key molecules: operando spectroscopy confirms that the Te center activates CO₂, and the Cu center helps to dissociate H₂O. The experimental and theoretical results reveal that the TeN₂–CuN₃ could cooperatively lower the energy barriers for the rate-determining step, promoting proton transfer kinetics. Therefore, the TeN₂–CuN₃ displays a broad potential range with high CO selectivity, improved kinetics and good stability. This work presents synthesis and characterization strategies for double-atomic site catalysts, and experimentally unveils the underpinning mechanism of synergistic catalysis.