Revisiting the Impact of Morphology and Oxidation State of Cu on CO 2 Reduction Using Electrochemical Flow Cell.

Electroreduction of carbon dioxide (CO 2 ) in a flow electrolyzer represents a promising carbon-neutral technology with efficient production of valuable chemicals. In this work, the catalytic performance of polycrystalline copper (Cu), Cu 2 O-derived copper (O(I)D-Cu), and CuO-derived copper (O(II)D-Cu) toward CO 2 reduction is unraveled in a custom-designed flow cell. A peak Faradaic efficiency of >70% and a production rate of ca. -250 mA cm -2 toward C 2+ products have been achieved on all the catalysts. In contrast to previous studies that reported a propensity for C 2+ products on OD-Cu in conventional H-cells, the selectivity and activity of ethylene-dominated C 2+ products are quite similar on the three types of catalysts at the same current density in our flow reactor. Our analysis also reveals current density to be a critical factor determining the C-C coupling in a flow cell, regardless of Cu catalyst's initial oxidation state and morphology.