Gold Decoration To Improve Rh-Nanoalloys for CO-Adsorption

After an accurate mapping of the available sites on Rh₁₉ and three different Rh₁₉Au _<i>M</i> nanoalloys (where <i>M</i> = 20, 36, or 52), the CO adsorption properties are obtained using density functional theory (DFT) at the PBE functional level, incorporating the Hubbard correction (PBE + <i>U</i>). The <i>U</i> values are selected to reproduce the correct adsorption trend and consistent binding of CO on Rh(111) in order to align with experimental measurements. The stabilization of the top adsorption site of CO, regarding the hollow one, is enhanced on the Rh₁₉ surface, compared to the Rh(111) surface. Our findings indicate that the strength of CO adsorption on small AuRh nanoparticles can be effectively tuned by varying their morphology and composition. The energy landscape of the Rh-based nanoalloys is relatively flat, with the adsorption energies at all sites varying within 0.3 eV, similar to the trend observed for Rh(111), although Rh sites in the nanoalloys generally bind CO more strongly. Adding Au shortens the CO-Rh bond, and sites with a mixed chemical environment result in instability. The presence of Rh enables Au-sites to bind CO twice as strongly as in Au(111).