Bimetallic electrocatalysts can improve the activity and selectivity over their monometallic counterparts by tuning the structure, morphology, and composition. However, there scarcely was a systematic model to understand the structural effect relationship on CO 2 electrochemical reduction reaction, especially for a product tuning process by introduction of a second metal to grow into outer layers. Herein, we report a structure-controlled model of the growth process of Ag@Cu bimetallic nanoparticles that are fabricated by a polyol method, that is, reducing mixtures of Ag + and Cu 2+ (excess amount) in ethylene glycol (reducing agent) in the presence of polyvinylpyrrolidone. Structural characterizations reveal that a series of Ag@Cu NPs are tuned from the Ag core, Cu modified Ag, to the Cu outer shell by controlling the heating time (0−25 min). Moreover, highly selective catalysts with the tuning reduction products from carbon monoxide to hydrocarbons can be realized. Different from the "dilution" effects between Ag and Cu, the volcanic curve for carbon monoxide production is detected for the introduction of Cu and the peak point is the Ag@Cu-7 electrocatalyst (heating time is 7 min). Similarly, interestingly, when the Cu cladding layer continuously grows, the hydrocarbons are not a simple proportional addition and optimized at Ag@Cu-20 (heating time is 20 min). The geometric effects dominantly account for the synergistic effect of CO product and control the surface activity to hydrocarbons. This study serves as a good starting point to tune the energetics of the intermediate binding to achieve even higher selectivity and activity for core−shell structured catalysts.

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As a key structural parameter, a crystal plane has a distinguished impact on the catalytic performance. Different exposed crystal planes exhibit different reactivities. CeO 2 nanostructured powders are usually exposed to three low-index surfaces, which are (111), (110), and (100) surfaces. Because of the unique structure and low stability of the (100) surface, the investigation of the catalytic reaction mechanism on this surface is rarely involved. Here, density functional theory calculations suggest that the CeO 2 (100) surface exhibits the strongest reactivity for H 2 oxidation, attributed to the coordination unsaturation of surface oxygen atoms. For the hydrogenation of CO 2 to methanol on the defective CeO 2 (100) surface, CO 2 is prone to adsorb at the oxygen vacancy in a nearly linear configuration and the formate pathway was verified as the dominant one. The bi-H 2 COO* can easily convert to bi-H 2 CO* with the vacancy site filled, in which bi-H 2 CO* serves as the key intermediate in the methanol synthesis. This study aims at providing a better understanding of the catalytic reactivity of the CeO 2 (100) surface and theoretical insights into the experimental design of thermal CO 2 -to-methanol conversion.