| 摘要: | 隨著全球氣溫上升和環境變化，控制大氣中的 CO2含量已成為全球環保目
標。電化學CO2還原反應(CO2RR)是一種將有害的CO2轉化為有價值燃料的有效策略。然而，CO2RR面臨許多挑戰，包括競爭性的析氫反應(HER)、選擇性和穩定性問題，導致CO2轉化效率低下，以及對貴金屬催化劑的依賴。
在本研究中，透過退火將Cu/C氧化為CuO/C以提高C2+產物的效率。X光
電子能譜(XPS)分析顯示，退火後結構轉變為CuO/C，同時表面產生了大量的氧空位(Ovac)，Ovac與晶格氧(Olat)的比值達到了3.2，高於Cu/C的1.8。因此，C2+產物的法拉第效率(FEC2+)在-1.1 V vs. RHE (VRHE)時達到 66.5%，分電流密度為14.4 mA/cm2，穩定性為10小時。而Cu/C在相同電壓下FEC2+只有59.4%且分電流密度也只有12.6 mA/cm2，表明 Ovac能夠提升銅基觸媒的活性與選擇性.透過原位X光吸收光譜進一步分析發現，與-1.2 VRHE相比，CuO/C在-1.1 VRHE時具有更多的不飽和配位，表明CuO/C的最佳工作電壓為-1.1 VRHE。 為了進一步調節選擇性，添加了少量的 Bi (Cu/Bi=99/1 和 98/2)。1% Bi@CuO/C 在-1.2 VRHE時的 CH4法拉第效率(FECH4)為42.3%，分電流密度為10.0 mA/cm2，穩定性為7小時。然而，2% Bi@CuO/C的FECH4下降到6.8%，而 FEHCOOH增加到33.8%。這表明Bi可以誘導電子轉移，顯著影響選擇性。XPS分析顯示，
1% Bi@CuO/C 的Ovac/Olat比值為 3.2，高於2% Bi@CuO/C的1.6，表明過量添加Bi 可能會減少Ovac活性位點的數量。原位X光吸收光譜進一步顯示，Bi的添加使工作電壓下的Cu-O和Bi-O鍵保持穩定，且Cu-Bi鍵的形成增強了催化性能。本研究強調，透過退火和少量Bi的添加可以增強銅基催化劑的催化活性，有效調節選擇性，並保持優異的穩定性。這為未來以碳氫化合物為目標的CO2RR催化劑設計提供了新的方向。;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. |
