Figure 4: Structural characterization of Au–Cu bimetallic nanoparticles.

(a) Surface valence band photoemission spectra of Au–Cu bimetallic nanoparticles. All the spectra are background corrected. The white bar indicates its centre of gravity. For comparison, the upper limit of integration is fixed to −9.0 eV in binding energy. (b) High-resolution transmission electron microscopy image of AuCu₃ and Au₃Cu, and their fast fourier transform. Scale bar, 5 nm. (c) X-ray photoemission spectra at grazing angle (85°) on Au–Cu bimetallic nanoparticle monolayers. See Supplementary Fig. 8 for the survey spectra. (d) Schematic showing the proposed mechanism for CO₂ reduction on the catalyst surface of Au–Cu bimetallic nanoparticles. Filled circles with grey is C, red is O and white is H. The relative intermediate binding strength is indicated by the stroke weight (on the top right corner). Additional binding between the COOH and the catalyst surface is presented as a dotted line. Arrows between the adsorbed COOH and adsorbed CO is to show the difference in probability of having COOH adsorbed on different types of surfaces. Coloured arrows indicate the pathway to each product: red for CO, blue for formate and green for hydrocarbons. Larger arrows indicate higher turnover.