(363o) Regulating C2 Product Yields in COx Hydrogenation By Fine-Tuning Palladium Atomicity in Pd-Cu Alloys

The electrocatalytic CO_x (CO₂ or CO) reduction reactions, termed CO_xRR, offer a sustainable method to convert CO_x emissions into value-added chemicals. The CO_xRR mechanism involves shared pathways through early *CO and *H (or protons). Achieving desired reactions requires *CO and *H to bind optimally on the catalyst, enabling proton-electron steps while preventing hydrogen evolution reaction (HER). Copper (Cu) stands out for its moderate binding energies to *H and *CO, making it uniquely capable of catalyzing the formation of various C₂ products but with limited specific yields. Palladium (Pd) offers some favorable attributes for CO_xRR that Cu lacks. For example, Pd shows favorable binding energies with *CO and is thus attractive for increasing CO coverage for C-C coupling, it also exhibits a lower affinity for oxygenate intermediates, thereby preserving oxygenates as final products. Despite these advantages, the exploration of Pd in CO_xRR is limited due to its strong *H adsorption capability on the extended surface to promote HER. We found alloying atomically dispersed Pd onto Cu surfaces offers the opportunity to adjust the binding strength of *CO, *H, and oxygenate groups without agitating the HER, thereby regulating the formation of C₂ products. Specifically, at the overpotential of -0.7 V vs. RHE, Pd₁Cu alloy with dilute single-atom Pd achieved over 65% ethylene Faradaic efficiency (FE) and a partial current density of 104 mA/cm². Differently, increasing single-atom Pd concentration to a crowded configuration on Cu made the alloy catalyst optimal for ethanol formation with FE over 80% and a partial current density of 266 mA/cm². Without any further increase of Pd loading but switching from single-atomto Pd dimers on Cu, acetate production was favored (55% FE, 174 mA/cm² partial current density). Our results showcase the rich design space at an atomistic level for Cu-based alloy catalysts, even without altering the nominal material formulations.