| dc.description.abstract | As the increasing demand for energy and the rising environmental pollution become global challenges, the electrochemical carbon dioxide reduction reaction (CO2RR) has emerged as a potential solution for reducing carbon emissions. CO2RR uses electric energy from sustainable energy sources to convert CO2 into high-value products, such as carbon monoxide (CO) and formic acid (HCOOH), offering a promising path towards true carbon neutrality. However, CO2RR faces several hurdles, including competition with the hydrogen evolution reaction, low CO2RR activity, and poor product selectivity. To address these issues, scientists have developed many binary catalysts, including copper (Cu) and tin (Sn) bimetallic catalysts, which exhibit strong synergistic effects in CO2RR. However, to improve the performance, the phases and compositions on binary catalysts needs further exploration and optimization.
In this study, Cu-SnO2/C and CuO-SnO2/C with the same atomic ratio of Cu/Sn = 99/1 were prepared. X-ray photoelectron spectroscopy analysis confirmed the electron transfer effect between Cu and Sn atoms. Under different voltages, Cu-SnO2/C and CuO-SnO2/C showed higher CO faradaic efficiency (FECO) than Cu/C, CuO/C, and SnO2/C, indicating that the synergistic effect between Cu/CuO and SnO2 could effectively suppress the HER reaction and enhance CO selectivity. Additionally, CuO-SnO2/C exhibited the best CO selectivity and stability, with a FECO of 95% at -0.8 V (vs. RHE) and maintaining 90% after 10 hours, compared to 80% for Cu-SnO2/C within 5 hours. These results indicate that the CuO-SnO2 interface demonstrates a superior synergistic effect compared to Cu-SnO2 interface, leading to the best improvement of CO selectivity and stability.
Furthermore, the relationship between the Cu/Sn atomic ratio and CO2RR performance was further explored. 99CuO-SnO2/C achieved a FECO of 95%, while the FECO of 13CuO-SnO2/C (Cu/Sn=93/7) only reached 46% and showed a FEHCOOH of 40%. In-situ X-ray absorption spectroscopy analysis revealed that the best CO selectivity of 99CuO-SnO2/C was due to the Sn-Cu bonding. When a small amount of Sn was added, numerous Sn-Cu bonds were formed. As the Sn content increased, Sn tended to aggregate and form Sn-Sn bonds, causing a shift in selectivity from CO to HCOOH. In addition, SnO2-modified CuO catalysts could prevent SnO2 from being reduced to Sn and maintain the activity site for CO2-CO conversion.
To confirm the synergistic effect between CuO and SnO2, physically mixed samples of CuO and SnO2 with Cu/Sn of 99/1 were prepared, which only achieved a FECO of 73% and maintained activity for 5 hours. This result highlights that physical mixing only produces limited synergistic effects, and a large number of CuO-SnO2 interfaces are crucial for achieving optimal CO2-CO conversion.
This study demonstrates the synergistic effect of CuO and SnO2 on CO2-CO conversion and investigates the impact of the atomic ratio on selectivity, providing new insights for catalyst design in CO2RR applications. | en_US |