A Precise Control of CO ₂ Electroreduction Pathways on Cu ₂ O Nanoparticles through Surface Facet and Microenvironment Modulation

Since facet-dependent reaction pathways are frequently disrupted by competitive hydrogen evolution reaction (HER) and reductive reconstruction, precisely controlling the selectivity of the electrocatalytic CO 2 reduction reaction (CO 2 RR) on CuO x -based catalysts remains challenging. In this paper, Cu 2 O nanoparticles (NPs) with explicitly exposed facets (100), mixed (100)/(111), and (111) were synthesized and further modified with the conductive polypyrrole (PPy) layer through an in-situ polymerization reaction to achieve the synergistic effect of crystal facet engineering and interfacial microenvironment. This approach enabled precise regulation of the CO 2 RR pathways on the Cu 2 O NPs. The experimental results showed that the PPy modification enhanced the CO 2 adsorption and hydrophobicity, effectively inhibiting HER and promoting the deep reduction of CO 2 . In the H-type cell with 0.1 mol/L KHCO 3 electrolyte saturated with CO 2, the Faraday efficiency (FE) of the PPy-c-Cu 2 O catalyst for the deeply reduced products reached 54.6%, while FE H2 decreased from 43.1 to 17.4%. All PPy-modified Cu 2 O catalysts with different exposed crystal facets exhibited enhanced CO selectivity in the flow cell. Quasi in-situ X-ray photoelectron spectroscopy showed that PPy modification prevented the active Cu(I) species from being reduced under cathode bias, enhanced stability, and enabled the FE of deeply reduced products to remain at 48.5% over 10 h. Density functional theory calculations indicated that PPy modification increased the *CO coverage on Cu 2 O (100) facets, reduced the C−C coupling barrier, and suppressed the HER process by raising the *H coupling energy barrier. This work provides experimental and theoretical guidance for the rational design of highly selective Cu 2 O catalysts.