Multi-products (C1 and C2) Formation from Electrochemical Reduction of Carbon Dioxide Catalyzed by Oxide-Derived Coppers Prepared Using Varied Synthesis Conditions

In order to explore the effects of morphology, specific surface area and relative content of Cu/Cu-oxide in “CuO-derived Cu” electrocatalysts on the current density and product formation during electrochemical carbon dioxide reduction reaction (eCO₂RR), CuO electrocatalysts were synthesized via solution combustion and hydrothermal routes, possessing different morphologies. The as-synthesized CuOs were first reduced to Cu at − 0.8 V (vs. RHE), till the currents got stabilized; thus, forming “CuO-derived Cu”. Subsequently, eCO₂RR was carried out via bulk electrolysis at different potentials between − 0.6 and − 1.6 V (using 0.1 M KHCO₃ solution), leading to the formation of seven liquid/gaseous products, viz., CO, methane, ethylene, formate, acetate, and ethanol (in addition to H₂). It was interesting to note that the type of products and associated faradic efficiencies (FEs) were governed by the Cu-content of the “CuO-derived Cu” electrocatalysts (i.e., Cu:CuO ratio), as obtained post the pre-reduction step and looked into here as one of the starting conditions of the electrocatalysts. Higher initial Cu-content of the pre-reduced CuOs resulted in higher FEs at lower negative potentials. Furthermore, high Cu-content (even for simple equiaxed morphology), as opposed to any special morphology (say, rod/whisker-type), has been found to be particularly important for the formations of methane and formate; yielding a maximum FE of ~ 18.6 ± 1.2% at − 1.0 V for the latter. Accordingly, the present work reveals the relative roles of specific surface area and Cu/CuO-content of “CuO-derived Cu” electrocatalysts on the current densities, product formation and associated FEs on eCO₂RR.

Graphical Abstract