Diluted Cu Sites in Pd-Cu Alloys Enable Selective CO2 to CO Conversion in Cation Exchange MEA

High-rate CO 2 electroreduction in cation exchange membrane (CEM)-based membrane electrode assemblies (MEAs) is practically advantageous because it is inherently free from carbonate crossover and anodic CO 2 loss, but it typically suffers from the parasitic hydrogen evolution reaction (HER). Here, we report highly selective CO production in optimized Nafion-based MEAs using Pd-Cu alloy nanoparticles with controlled composition and atomic ordering. We evaluated a series of Pd-Cu catalysts, finding that Pd 3 Cu 1 achieved a maximum CO Faraday efficiency (FE) of 74.7% at 200 mA/cm 2 (3.58 V). Crucially, the impact of atomic ordering was revealed by comparing Pd 1 Cu 1 structures: the B2-ordered phase exhibited 66.2% FE to CO, whereas the disordered A1 phase yielded only 26.7% CO, with concurrent C 2 H 4 and CH 4 production. These results could suggest that diluted Cu sites in the Pd matrix facilitate CO desorption, while contiguous Cu-Cu ensembles drive C-C coupling. This study provides a geometric catalyst design strategy for optimizing product selectivity in commercially relevant CEM-MEA CO 2 electrolyzers.