Synthesis of Cu2O Nanostructures with Tunable Crystal Facets for Electrochemical CO2 Reduction to Alcohols

Electrochemical CO2 reduction enables the conversion of intermittent renewable energy to value-added chemicals and fuel, presenting a promising strategy to relieve CO2 emission and achieve clean energy storage. In this work, we developed nanosized Cu2O catalysts using the hydrothermal method for electrochemical CO2 reduction to alcohols. Cu2O nanoparticles (NPs) of various morphologies that were enclosed with different crystal facets, named as Cu2O-c (cubic structure with (100) facets), Cu2O-o (octahedron structure with (111) facets), Cu2O-t (truncated octahedron structure with both (100) and (111) facets), and Cu2O-u (urchin-like structure with (100), (220), and (222) facets), were prepared by regulating the content of a polyvinyl pyrrolidone (PVP) template. The electrochemical CO2 reduction performance of the different Cu2O NPs was evaluated in the CO2-saturated 0.5 M KHCO3 electrolyte. The as-synthesized Cu2O nanostructures were capable of reducing CO2 to produce alcohols including methanol, ethanol, and isopropanol. The alcohol selectivity of the different Cu2O NPs followed the order of Cu2O-t < Cu2O-u < Cu2O-c < Cu2O-o (with the total Faradaic efficiencies of alcohol products of 10.7, 25.0, 26.2, and 35.4%). The facet-dependent effects were associated with the varied concentrations of oxygen-vacancy defects, different energy barriers of CO2 reduction, and distinct Cu-O bond lengths over the different crystal facets. The desired Cu2O-o catalyst exhibited good reduction activity with the highest partial current density of 0.51 mA/cm(2) for alcohols. The Faradaic efficiencies of alcohol products were 4.9% for methanol, 17.9% for ethanol, and 12.6% for isopropanol. The good electrochemical CO2 reduction performance was also associated with the surface reconstruction of Cu2O, which endowed the catalyst with abundant Cu-0 and Cu+ sites for promoted CO2 activation and stabilized CO* adsorption for enhanced C-C coupling. This work will provide a new route for enhancing the alcohol selectivity of nanostructured Cu2O catalysts by crystal facet engineering.