Surface composition dominates the electrocatalytic reduction of CO2 on ultrafine CuPd nanoalloys

Preciously tuning the surface composition of noble metal nanoparticles with the particle size of only 2nm or less by alloying with other metals represents a powerful strategy to boost their electrocatalytic selectivity. However, the synthesis of ultrafine nanoalloys and tuning their surface composition remain challenging. In this report, ultrafine CuPd nanoalloys with the particle size of ca. 2nm are synthesized based on the galvanic replacement reaction between presynthesized Cu nanoparticles and Pd2+ precursors, and the tuning of their surface compositions is also achieved by changing the atom ratios of Cu/Pd. For the electrocatalytic reduction of CO2, Cu5Pd5 nanoalloys show the CO Faradaic efficiency (FE) of 88% at -0.87V, and the corresponding mass activity reaches 56A/g that is much higher than those of Cu8Pd2 nanoalloys, Cu3Pd7 nanoalloys and most of previously reported catalysts. Density functional theory uncovers that with the increase of Pd on the surface of the ultrafine CuPd nanoalloys, the adsorbed energy of both of intermediate COOH* and CO* to the Pd sites is strengthened. The Cu5Pd5 nanoalloys with the optimal surface composition better balance the adsorption of COOH* and desorption of CO*, achieving the highest selectivity and activity. The difficult liberation of absorbed CO* on the surface of Cu3Pd7 nanoalloys provides carbon source to favor the production of ethylene, endowing the Cu3Pd7 nanoalloys with the highest selectivity for ethylene among these ultrafine CuPd nanoalloys.