| 摘要: | 二氧化碳的電化學還原反應(carbon dioxide electrochemical reduction reaction, CO2RR)是減少大氣中CO2最有效的方法之一，並可同時生產工業上所需的燃料或化學品。然而，CO2RR觸媒所面臨到的挑戰包含：與析氫反應(hydrogen evolution reaction, HER）的競爭，所需的過電位高，CO2RR活性低，產物選擇性差且成本高。為了解決上述問題，目前科學家們已經開發了許多二元觸媒。透過第二種材料的添加，改變反應中間體的結合能，從而提高CO2RR的活性和選擇性。
本研究選擇低成本的材料：銅(copper, Cu)和氧化銦(indium oxide, In2O3)。為了找到最佳的比例，製備不同的Cux(In2O3)y/C奈米顆粒，其Cu/In2O3比例分別為96/4、85/15、72/28和36/64。X射線光電子能譜(X-ray photoelectron spectroscopy, XPS)的分析結果證實了Cu核-In2O3殼的結構形成。在-0.7 V (vs. RHE)下，Cu96(In2O3)4/C的一氧化碳(carbon monoxide, CO)法拉第效率為95%，遠遠超過Cu/C的18%和In2O3/C的13%。Cu96(In2O3)4/C也具有極好的CO質量活性，其為-642 A gIn-1，而In2O3/C僅有-8 A gIn-1。在CO2RR穩定性測試中，Cu96(In2O3)4/C可以保持優異的CO法拉第效率長達7小時。另外，根據CO剝離(CO stripping)的測試結果，發現表面添加In2O3可以降低CO的吸附能，使產物CO更容易脫附。在原位X光吸收光譜(in-situ X-ray absorption spectroscopy, in-situ XAS)結果中，推測In2O3殼層可防止Cu核氧化，並擋住HER的活性位點；而其在CO2RR的過程中In2O3殼明顯地被還原。以上結果皆表明具有核殼結構的二元觸媒可以達到CO2RR反應中的高選擇性和活性。另外，製備了Cu和In2O3的物理混合物，可達67%的CO法拉第效率。本研究經由Cu96(In2O3)4中兩種材料的結合，將產甲酸的In2O3和產氫氣的Cu結合後轉變為產CO，透過調整二元比例和核殼結構，達到最佳化的CO選擇性、活性和穩定性。;Electrochemical reduction reaction of carbon dioxide (CO2RR) is one of the most promising solutions to mitigate the global CO2 emission and produce useful fuels or chemicals simultaneously. However, the serious challenges for the catalysts of electrochemical CO2RR involve the competition with hydrogen evolution reaction (HER), high overpotentials required, low CO2RR activity, poor products selectivity, and high cost. In order to solve the above problems, many binary catalysts have been developed because the binding energy of reactive intermediate is changed due to the second metal addition, further promoting the CO2RR selectivity and activity.
In this study, the low-cost materials like copper (Cu) and indium oxide (In2O3) are selected. In order to find the best Cu/ In2O3 ratio, the carbon-supported Cux(In2O3)y nanoparticles with Cu/In2O3 ratios of 96/4, 85/15, 72/28, and 36/64 have been prepared. The results of X-ray photoelectron spectroscopy (XPS) confirms the formation of Cu core - In2O3 shell structure. Among the catalysts, Cu96(In2O3)4/C has exhibited the best CO faradaic efficiency of 95 %, far more than 18 % of Cu/C and 13 % of In2O3/C at - 0.7 V (vs. RHE), and the super excellent CO mass activity of -642 A gIn-1, compared with -8 A gIn-1 of In2O3/C. Moreover, the CO2RR stability test shows that Cu96(In2O3)4/C can remain high CO faradaic efficiency for 7 h. According to the CO stripping results, the binding energy of CO is diminished with the addition of In2O3 on the surface because Cu can form *CO easily, and In2O3 can promote CO desorption. Moreover, the in-situ X-ray absorption spectroscopy (XAS) results displays that In2O3 shell prevents Cu core from oxidation and obstructs their HER active sites while it reduces obviously during CO2RR. These results reveal that the binary catalysts with core-shell structure can achieve high selectivity and activity. In addition, physical mixture of Cu and In2O3 has been prepared, reaching CO faradaic efficiency of 67%. It is believed that the transformation of product selectivity from HCOOH for In2O3 and H2 for Cu to CO for Cu96(In2O3)4/C, and the optimization of the CO selectivity, activity, and stability stem from the binary effect and core-shell structure. |
