Physical vapor deposition was performed to obtain a 100-nm Cu(100) film epitaxially grown onto Si(100) substrate, followed by introducing 1-Å-equivalent another metal M (M: Ag, Au, In, Mo, Ni, Pd, and Sn) atoms onto the Cu(100) surface in vacuum. Atomic force microscopy and X-ray photoelectron spectroscopy guaranteed that M certainly existed on Cu and the M/Cu electrocatalyst had a smooth surface whose roughness was ±2 nm. The M/Cu electrocatalyst was supplied to a series of 15-min electrolysis in 0.1 mol dm−3 KHCO3 aqueous solution at potentials ranging from −0.6 to −1.1 V with respect to reversible hydrogen electrode at pH 6.8. Gaseous and liquid products were quantified with gas chromatography and nuclear magnetic resonance, respectively.
A series of electrocatalytic evaluation pointed out the following general trends concerning the electrocatalytic properties of the M/Cu bimetallic thin films for CO2RR. For selectivity, the M atoms introduced to Cu(100) surface vary the Faradaic efficiency for each product to decrease average number of electrons transferred to a CO2 molecule. For activity, the introduction of M atoms onto Cu(100) surface suppresses the production rates for both C1 and C2+ products although it increases or decreases the total current density as seen in cyclic voltammetry, depending on M. The aforementioned experimental facts suggest the role of M that the M atoms introduce onto Cu(100) surface seem to cause some bimetallic effects on the CO2RR selectivity of Cu as well as an inhibition effect on the CO2RR activity of Cu. Electron-transfer reaction kinetics are further studied via a combined experiment and theory approach to discuss the nature of active sites in M/Cu bimetallic systems and the role of M in determining product distribution, which will be explained in the conference.