Synthesis of CuO Nanostructures with Tunable Crystal Facets for Electrochemical CO Reduction to Alcohols.

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