| 摘要: | 由於全球工業化的發展，導致大量二氧化碳排放所造成的環境災害已經是個嚴重的問題，因此再生能源的研究已經成為當今的熱門議題，而電化學還原二氧化碳反應 (carbon dioxide electrochemical reduction reaction, CO2RR) 因可將二氧化碳轉化成高價值化學燃料，為一改善二氧化碳排放的有效方法，但CO2RR主要問題是與其競爭的析氫反應（hydrogen evolution reaction, HER），這會導致較差選擇性和法拉第效率，因此本研究以銅為基底，目標開發出高活性、高選擇性以及長期穩定性的觸媒。
本研究分成兩個部分，第一部分使用對一氧化碳產物具有高選擇性的金形成銅基內核/金富含於外表層之奈米觸媒，可得到高質量活性並進一步添加第三金屬鋅，使其因增強協同作用以達到效能穩定，利用高解析度穿透式電子顯微鏡(high resolution transmission electron microscopy, HRTEM)、感應耦合電漿原子發射光譜分析儀(inductively coupled plasma-optical emission spectrometer, ICP-OES) 及X光繞射儀(X-ray diffraction, XRD) 證實其為非均相的三元奈米觸媒，根據一氧化碳剝離試驗(CO stripping)及X光電子能譜儀 (X-ray photoelectron spectroscopy, XPS)的結果，由於表面金的添加，弱化了中間產物一氧化碳的吸附能，但第三金屬鋅的添加又使CO吸附能上升，在電化學上，Au/C擁有最低的起始電位(-0.5 V)，而在-0.8 V下Cu8Au2/C具有94 %的一氧化碳法拉第效率及最高的質量活性394.1 A/gAu-1，但其穩定度不佳，Cu8Au2/C的一氧化碳法拉第效率和質量活性分別衰退了26.5和58.9 %，而Cu8Au2Zn0.3/C和Cu8Au2Zn1.2/C在經過六小時的電化學穩定度試驗後，一氧化碳法拉第效率和質量活性分別只衰退2.2和12.4 % 與0.3和6.3 %，結果表明加入鋅作為第三元素可以增長觸媒穩定度。
第二部分合成二元Cu6Zn4/C和三元Cu8Au2Zn1.2/C及Cu7Ag2Zn1.2/C，在電催化CO2RR的效能表現上，相較於二元觸媒Cu6Zn4/C，三元觸媒Cu8Au2Zn1.2/C及Cu7Ag2Zn1.2/C展現最低的CO起始反應電位(-0.5 V)並且整體CO法拉第效能上升分別為46.4和80.1 %，並且Cu7Ag2Zn1.2/C在長時間-1.1 V，CO的法拉第效率可以維持75到80 %二十小時以上，本研究揭示了藉由形成二元銅基奈米觸媒可降低貴金屬的添加並且經由電子修飾效應達到高的一氧化碳選擇性與活性，並且在添加第三元素形成三元奈米觸媒之後，雖然損失部分活性，但觸媒整體的穩定性獲得提升。
;Due to the development of global industrialization, the environmental disaster caused by a large amount of carbon dioxide emissions has been a serious problem. The research to develop renewable energy has become a hot topic today. The carbon dioxide electrochemical reduction reaction (CO2RR) is a promising method to reduce carbon dioxide emissions through the conversion of CO2 into high-value chemical fuels. However, the main problem of CO2RR is the competitive hydrogen evolution reaction (HER), which will lead to poor selectivity and Faraday efficiency. Therefore, in this study, the preparation and promotion of Cu-based binary and ternary catalysts with high activity, high selectivity and long-term stability have been elucidated.
This study is divided into two parts. Au with high selectivity for carbon monoxide is used to form Cu-based in the inner core/Au-rich on the outer shell structure, showing high mass activity (MA). Moreover, in order to further improve the stability, Zn is added to form ternary nanocatalysts. High resolution transmission electron microscope (HRTEM), inductively coupled plasma-optical emission spectrometer (ICP-OES) and X-ray diffraction (XRD) confirmed that they are heterogeneous ternary nanocatalysts. According to the results of carbon monoxide stripping test (CO stripping) and X-ray photoelectron spectroscopy (XPS), when Au is added, the adsorption energy of the carbon monoxide intermediate decreases, but after the addition of Zn, the CO adsorption energy rises. For the CO2RR, Au/C has the lowest onset potential (-0.5 V), while at -0.8 V Cu8Au2/C has a 94% carbon monoxide Faraday efficiency and the highest MA of 394.1 A gAu-1, but the stability is not good enough, in which there is a 26.5 and 58.9 % decay for CO Faraday efficiency (CO FE) and MA of Cu8Au2/C, respectively. On the other hand, for Cu8Au2Zn0.3/C and Cu8Au2Zn1.2/C, after 6 h of electrochemical stability test, their CO FE and MA of carbon monoxide only decay 2.2 and 12.4% and 0.3 and 6.3%, respectively, showing that the third element addition can enhance the stability of the catalysts.
In the second part, binary Cu6Zn4/C, and ternary Cu8Au2Zn1.2/C and Cu7Ag2Zn1.2/C are synthesized. In terms of the electrochemical CO2RR performance, compared with the binary Cu6Zn4/C, the ternary Cu8Au2Zn1.2/C and Cu7Ag2Zn1.2/C exhibit the lowest CO onset potential (-0.5 V) and CO FE increase to 46.4 and 80.1%, respectively. Moreover, CO FE of Cu7Ag2Zn1.2/C can be maintained from 75 to 80% for more than 20 h at -1.1 V (RHE). This study reveals that the formation of Cu-based binary nanocatalysts can reduce the amount of noble metals addition and achieve high CO selectivity and activity through the electron modification effect, and after adding a third element to form ternary nanocatalysts, although with some activity and selectivity loss, the overall stability of the catalysts is improved. |
