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

Abstract Preciously tuning the surface composition of noble metal nanoparticles with the particle size of only 2 nm 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. 2 nm 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 −0.87 V, and the corresponding mass activity reaches 56 A/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.