Electrochemical Fragmentation of Cu₂O Nanoparticles Enhancing Selective C-C Coupling from CO₂ Reduction Reaction

In this study, we demonstrate that the initial morphology of nanoparticles can be transformed into small fragmented nanoparticles, which were densely contacted to each other, during electrochemical CO₂ reduction reaction (CO₂RR). Cu-based nanoparticles were directly grown on a carbon support by using cysteamine immobilization agent, and the synthesized nanoparticle catalyst showed increasing activity during initial CO₂RR, doubling Faradaic efficiency of C₂H₄ production from 27% to 57.3%. The increased C₂H₄ production activity was related to the morphological transformation over reaction time. Twenty nm cubic Cu₂O crystalline particles gradually experienced in situ electrochemical fragmentation into 2-4 nm small particles under the negative potential, and the fragmentation was found to be initiated from the surface of the nanocrystal. Compared to Cu@CuO nanoparticle/C or bulk Cu foil, the fragmented Cu-based NP/C catalyst achieved enhanced C₂₊ production selectivity, accounting 87% of the total CO₂RR products, and suppressed H₂ production. In-situ X-ray absorption near edge structure studies showed metallic Cu⁰ state was observed under CO₂RR, but the fragmented nanoparticles were more readily reoxidized at open circuit potential inside of the electrolyte, allowing labile Cu states. The unique morphology, small nanoparticles stacked upon on another, is proposed to promote C-C coupling reaction selectivity from CO₂RR by suppressing HER.