Since the first development of synthetic plastics, people have been getting a variety of plastics mainly from petroleum, which drove modern civilization. Typically, polyethylene is the most frequently and widely used plastic. But the depletion of fossil fuels and the simultaneous increase in the concentration of carbon dioxide(CO2), which is at a dangerous level, have led to the need to reduce petroleum use and to reduce CO2. The conversion of CO2 to ethylene, the raw material for polyethylene, is a very promising strategy for achieving that. Electrochemically, ethylene can be obtained by reducing CO2 using sustainable electricity. Cu is reported to be the only single element catalyst that is capable of producing hydrocarbons with more than one carbon such as ethylene(C2H4) from CO2. It is because Cu has moderate intermediate binding energy. However, pure Cu catalyst represents poor C2H4 production efficiency because of the activity and selectivity problem. Therefore, alloying Cu with other elements can be one of the best strategy to enhance the activity and selectivity of the catalysis. However, conventional strategy to alloy Cu with other elements and modify the d-orbital energy failed to enhance selectivity for C2H4 because of the scaling relationship between binding energy of intermediates. In this work, controlled microstructure of binary alloy was investigated as a new strategy for selective C2H4 production. Based on the thermodynamic database, the microstructure of Cu-X alloy was carefully designed. By adopting the terminal solid solution system, in which phase segregation take place, unlike conventional homogeneous solid solution system, the microstructure of the alloy consisting of lamellar structure could be controlled. In that system, different binding affinities with intermediates of segregated phases were taken advantage of. The synergetic effect between different phases was investigated by controlling the density of phase boundaries based on the understanding on metallurgy of alloy system. As the result, the selectivity for C2H4 increased with the increase of the density of phase boundary, which suggests the CO spillover between CO-selective phase and Cu and the following CO-CO dimerization. This work provided new catalyst design strategy for efficient electrochemical CO2 conversion to targeted chemicals.