Preparing supported nanoparticles with a well-defined structure, uniform particle size, and composition using conventional catalyst synthesis methods, such as impregnation, precipitation, and deposition-precipitation is challenging. Furthermore, these liquid phase methods require significant solvent consumption, which has sustainable issues and requires complex purification processes, usually leaving impurities on the catalyst, affecting its selectivity and activity. In this work, we employed atomic layer deposition (ALD, a vapor phase synthesis method) to synthesize electrocatalysts with well-controlled core-shell and alloy structures for CO₂ reduction to formic acid. With this approach, the structural control of the catalysts is down to the atomic scale, and the effect of core-shell and alloy structure on Pt−Pd bimetallic catalysts has been investigated. It is shown that the Pt−Pd alloy catalyst displays a 46 % faradaic efficiency toward formic acid, outperforming Pt@Pd and Pd@Pt core-shell structures that show faradaic efficiencies of 22 % and 11 %, respectively. Moreover, both core-shell bimetallic catalysts (Pd@Pt and Pt@Pd) are not stable under electroreduction conditions. These catalysts restructure to more thermodynamically stable structures, such as segregated clusters or alloy particles, during the electrochemical reduction reaction, altering the catalytic selectivity.