Revealing the Reaction Mechanism of C-C Coupling on Cu-based Tandem Catalysts towards CO2 Reduction

Abstract

Cu-based tandem catalysts have widely been exploited to improve the catalytic performance for multi-carbon (C2+) products towards CO2 electroreduction. Nevertheless, the underlying reaction mechanism for tandem catalytic system remains ambiguity. Herein, we unraveled the relationship between the behavior of adsorbed CO intermediate (*CO) and the process of C-C coupling. Due to the low coverage of *CO, the process of C-C coupling has always been restricted for Cu catalysts. Through regulating the molar ratios of CO2 to CO in co-feeding gases, we found that the moderate surface coverage of *CO was beneficial for the electroreduction of CO2 into ethylene (C2H4). Meanwhile, the cross-coupling process between CO2 and CO was proved to be responsible for the enhanced activity of C2H4 according to isotopic labeling experiments. We constructed a tandem model with cobalt phthalocyanine (CoPc) as CO-generating component on Cu to further verify the tandem mechanism. With the introduction of CoPc onto the surface of Cu, the partial current density for C2H4 reached as high as 313 mA cm-2 at applied current density of 480 mA cm-2, which was one-fold higher than that (165 mA cm-2) of Cu film. In-situ Raman measurements further revealed that CO generated by CoPc increased the coverage of *CO on the surface of Cu, facilitating the process of C-C coupling.