Electroreduction of CO2 represents a promising approach toward artificial carbon recycling. Copper (Cu) has been known as the only metal that catalyzes C-C coupling in the electroreduction of CO2 and CO toward value-added C2+ hydrocarbon products such as ethylene, ethanol, acetate and n-propanol. To achieve electrocatalytic performance super to pure Cu, extensive efforts have been devoted to alloy or single-atom electrocatalysts for CO2 and CO reduction, but how atomic ensembles of active sites interplay with the C-C coupling mechanisms remains largely elusive. This presentation aims to introduce our efforts on the development of advanced alloy electrocatalysts for CO2 and CO reduction. Topics to be covered include i) alloy electrocatalysts such as Pdn@Au and random Pd-Cu bimetallics and ii) single-atom Cu1@C3N4 for CO2 or CO reduction to C2 hydrocarbons. Atomic structures of these electrocatalysts are characterized by using state-of-the-art electron microscopy and X-ray spectroscopy techniques. Surface structures and adsorption properties of the electrocatalysts are probed by measuring temperature- or potential-programed chemisorption of small molecules (e.g., COad and OHad). Kinetic analysis is performed to discern the rate-determining factors and reaction pathways. The established structure-property-performance correlations are further subjected to computational simulations to develop fundamental understanding of the catalytic mechanisms. Our work highlight the great potential of utilizing CO2 as the feedstock for renewable synthesis of hydrocarbon chemicals.