Synergistic effect of Cu and Ru decoration on g-C3N4 for electrocatalytic CO2 reduction

Electrocatalytic CO2 reduction is an emerging approach for the reduction of CO2 in a feasible, green, and effective manner. In this study, bimetallic compounds of Cu and Ru were both decorated onto a π-conjugated g-C3N4 surface (CuxRuyCN), which functioned as an electrode for electrochemical CO2 reduction. From the X-ray photoelectron and X-ray absorption spectra, Cu and Ru on CuxRuyCN were identified as the oxidative states of CuO/Cu2O and RuO2, respectively. The mixed states of CuO and Cu2O served as active sites to both adsorb and activate CO2 for effective reduction, while RuO2 synergistically served as the hole-enrichment center and transferred H protons to promote CO2 reduction. Consequently, the electrochemical current density of CuxRuyCN was significantly enhanced compared with the corresponding densities of CN or Cu-doped CN. The current density of CuxRuyCN reduced to less than −0.05 mA cm−2 at an applied voltage of −1.5 V in an air or Ar atmosphere, indicating that the high current density of CuxRuyCN was associated with the flow of CO2 and its reduction. Moreover, the current density of CuxRuyCN was maintained at approximately −0.3 mA cm−2 for at least 2000 s at an applied voltage of −1.4 V (vs Ag/AgCl), indicating its high stability during CO2 reduction. In summary, both Cu and Ru-modified g-C3N4 samples used to produce CuO/Cu2O- and RuO2-decorated g-C3N4 acted as effective catalysts for electrocatalytic CO2 reduction and demonstrated several potential electrochemical applications.