| dc.description.abstract | As global temperatures rise and environmental changes occur, controlling atmospheric carbon dioxide (CO2) levels has become a worldwide environmental goal. Electrochemical CO2 reduction reaction (CO2RR) is an effective strategy to convert harmful CO2 into valuable fuels. However, CO2RR faces several challenges, including the competitive hydrogen evolution reaction (HER), selectivity and stability issues
leading to low CO2 conversion efficiency, and reliance on noble metals catalysts. In this study, Cu/C was oxidized to CuO/C to enhance the efficiency of C2+ products. X-ray photoelectron spectroscopy (XPS) analysis revealed that after annealing, the structure transformed into CuO/C with the surface generating numerous oxygen vacancies (Ovac), and the ratio of Ovac to lattice oxygen (Olat) reached 3.2, higher than 1.8 for Cu/C. As a result, the Faradaic efficiency of C2+ products (FEC2+) at -1.1 V vs. RHE (VRHE)reaches 66.5%, with a partial current density of 14.4 mA/cm2 and the stability of 10 hours. Under the same voltage, Cu/C exhibited only 59.4% FEC2+ and a
partial current density of 12.6 mA/cm², indicating that Ovac can enhance the activity and selectivity of Cu-based catalysts. Further analysis by in-situ X-ray absorption
spectroscopy (in-situ XAS) indicated that CuO/C confirmed more unsaturated coordination at -1.1 VRHE compared to -1.2 VRHE, suggesting that the optimal operating voltage for CuO/C is -1.1 VRHE. To further tune the selectivity, a low amount of Bi was added (Cu/Bi=99/1 and 98/2). The 1% Bi@CuO/C achieved a CH4 Faradaic efficiency (FECH4) of 42.3% at -1.2 VRHE, with a partial current density of 10.0 mA/cm2 and stability of 7 hours. However, the FECH4 of 2% Bi@CuO/C decreased to 6.8%, while the FEHCOOH increased to 33.8%.
This indicates that Bi can induce electron transfer, significantly influencing selectivity. XPS analysis showed that the Ovac/Olat ratio for 1% Bi@CuO/C was 3.2, higher than 1.6 for 2% Bi@CuO/C, indicating that excessive Bi addition could reduce the number of Ovac active sites. In-situ XAS further revealed that the addition of Bi maintained the stability of Cu-O and Bi-O bonds under operating voltage, and the formation of Cu-Bi bonds enhanced the catalytic performance. This study highlights that annealing and the addition of a low amount of Bi can enhance the catalytic activity of Cu-based catalysts, effectively modulate selectivity, and maintain excellent stability. It provides a new direction for future CO2RR catalyst design targeting hydrocarbon production. | en_US |