Unravelling the influence of shell thickness in organic functionalized Cu2O nanoparticles on C2+ products distribution in electrocatalytic CO2 reduction

Abstract: Cu-based electrocatalysts exhibits enormous potential for electrochemical CO2 conversion to added-value products. However, high selectivity, specially towards C2+ products, remains a critical challenge for its implementation in commercial applications. Herein, we report the preparation of a series of electrocatalysts based on octadecyl amine (ODA) coated Cu2O nanoparticles. HRTEM images show ODA coatings with thickness from 1.2 to 4 nm. DFT calculations predict that at low surface coverage, ODA tends to lay on the Cu2O surface, leaving hydrophilic regions. Oppositely, at high surface coverage, the ODA molecules are densely packed, being detrimental for both mass and charge transfer. These changes in ODA molecular arrangement explain differences in product selectivity. In situ Raman spectroscopy has revealed that the optimum ODA thickness contributes to the stabilization of key intermediates in the formation of C2+ products, especially ethanol. Electrochemical impedance spectroscopy and pulse voltammetry measurements confirm that the thicker ODA shells increase charge transfer resistance, while the lowest ODA content promotes faster intermediate desorption rates. At the optimum thickness, the intermediates desorption rates are the slowest, in agreement with the maximum concentration of intermediates observed by in situ Raman spectroscopy, thereby resulting in a Faradaic efficiency to ethanol and ethylene over 73 %.