Electrochemical CO2 Reduction on Bimetallic Surface Alloys: Enhanced Selectivity to CO for Co/Au(110) and to H2 for Sn/Au(110)

We investigated electrochemical CO2 reduction (ECR) on 0.1 monolayer‐thick‐Co and Sn‐deposited Au(110) surfaces (Co/Au(110), and Sn/Au(110)). Scanning tunneling microscopic images showed quasi‐one‐dimensional Co and Sn islands with different aspect ratios growing along the trenches of the missing‐row direction of the (1×2) reconstructed Au(110) surface. The selectivity and partial current density of the CO and H2 evolutions correlated with those of the deposited metals. CO evolution selectivity of the former Co/Au(110) increased compared with that of the Au(110), while that of the Sn/Au(110) significantly decreased. Co/Au(110) showed 1.4‐fold higher CO evolution activity than that of the clean Au(110) at −1.35 V vs. reversible hydrogen electrode. In contrast, the H2 evolution of the latter surface was significantly enhanced at a potential lower than −0.1 V. The results showed that site separations of Au and alloying elements of Co and Sn at the topmost surface determine the ECR product selectivity of alloy electrodes. Surface engineering: Electrochemical CO2 reduction on Co/Au(110) and Sn/Au(110) surface alloys is investigated by using online electrochemical mass spectrometry. Co effectively improves the selectivity and activity for CO generation, while Sn increases the hydrogen evolution reaction activity of Au.