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.