碳支撐錫基奈米觸媒應用於電催化二氧化碳還原甲酸之研究;Carbon-Supported Sn-based Bimetallic Catalysts Applied for Electrochemical Reduction of CO2 to Formate

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Title:	碳支撐錫基奈米觸媒應用於電催化二氧化碳還原甲酸之研究;Carbon-Supported Sn-based Bimetallic Catalysts Applied for Electrochemical Reduction of CO2 to Formate
Authors:	林詩芳;Lin, Shih-Fang
Contributors:	材料科學與工程研究所
Keywords:	二氧化碳還原反應;銀;錫;甲酸;法拉第效率;協同效應;CO2 reduction reaction (CO2RR);Ag;Sn;formate;faradaic efficiency (FE);synergistic effect
Date:	2022-01-06
Issue Date:	2022-07-13 18:28:53 (UTC+8)
Publisher:	國立中央大學
Abstract:	由於大氣中二氧化碳濃度的增加導致全球暖化，明顯地改變氣候和自然生態的平衡。因此，透過二氧化碳的電化學還原反應(carbon dioxide electrochemical reduction reaction, CO2RR) 生產高附加價值的化學品被認為是實現碳循環的途徑之一。然而，電化學CO2RR面臨的挑戰在於其與析氫反應(hydrogen evolution reaction, HER)的競爭和產物選擇性不佳。因此，設計和製備具有低過電位、高法拉第效率和高選擇性的觸媒是CO2RR技術發展的關鍵考量因素。本研究分為兩個部分。在第一部分，製備了In/Sn原子比為 3/1 和 1/1 的In-Sn二元觸媒。In-Sn奈米顆粒的結構為In、In(OH)3和少量InSn4，而表面有些許的In(OH)x和SnOx。表面In(OH)3不僅有效抑制HER以提高CO2RR活性，並與CO2相互作用形成In-CO3-物種並還原為甲酸。因此，InxSny奈米顆粒展現出優異的性能。在-1.0 V下，甲酸法拉第效率為92.6 %，且實現了10小時的出色穩定性。在第二部分，設計了一系列Ag-Sn二元奈米顆粒應用於CO2RR。觸媒結構主要由Ag、Ag3Sn和SnO2組成，並且有少量 Ag 氧化物和大量 SnOx在觸媒表面。表面的氧化錫，為形成甲酸的主要活性位點。根據電化學結果，Ag觸媒的一氧化碳法拉第效率為94.9 %，也不產出任何甲酸產物，而SnO2 的甲酸法拉第效率為71.0 %。有趣的是，Ag4Sn展現最佳的甲酸選擇性，在-1.0 V下，具有最高的甲酸法拉第效率為90.9 %和分電流密度為-4.64 mA cm-2。此外，在CO2RR穩定性測試中，可以保持優異的甲酸法拉第效率長達10小時，證明其對電化學CO2RR形成甲酸的潛力。基於上述結果，產物選擇性的轉變、HCOOH選擇性、活性和穩定性的優化源於Ag-Sn中金屬和氧化物在電催化中的協同作用。本研究對於通過優化Sn基奈米顆粒的組成和結構以提高CO2RR選擇性的方法提供了指引方針。;The increasing concentration of CO2 in the atmosphere leads to global warming, which greatly changes the climate and the ecological balance of nature. Therefore, electrochemical CO2 reduction reaction (CO2RR) to produce highly value-added products is regarded as a prospective path toward carbon cycling. However, the challenges in electrochemical CO2RR are its competition to hydrogen evolution reaction (HER) and unsatisfied products selectivity. Therefore, the design and preparation of highly effective catalysts with low overpotential, high faradaic efficiency (FE), and high selectivity is key consideration for the development of CO2RR technology. This research is divided into two parts. In the first part, the binary In-Sn catalysts with In/Sn atomic ratios of 3/1 and 1/1 have been prepared. In -Sn nanoparticles (NPs) are composed of In, In(OH)3 and few InSn4 with some surface In hydroxides and Sn oxides. The catalyst with surface In hydroxide not only effectively suppresses the HER to increase the CO2RR activity but also interacts with CO2 to form In-CO3- species which then is reduced to formate. Therefore, the InxSny NPs show outstanding performance with a HCOOH FE of 92.6 % and excellent durability for 10 h at -1.0 V. In the second part, a series of Ag-Sn binary NPs was designed for CO2RR. Structural characterizations reveal that the existence of Ag, Ag3Sn and SnO2 with few surface Ag oxides and many surface SnOx. The surface SnOx is the major active site in the formation of formate. According to the electrochemical results, Ag catalyst exhibits high CO FE of 94.9 %, without any formate products while SnO2 shows the formate FE of 71.0 %. It is interesting to find that Ag4Sn particularly shows excellent catalytic CO2RR to formate, with maximum formate FE of 90.9 % and partial current density of -4.64 mA cm-2 at the overpotential of -1.0 V (vs.RHE). Moreover, the catalytic activity of Ag4Sn remains reasonably stable over a 10 h period of electrolysis, demonstrating its potential for electrochemical CO2RR to formate. Based on the above results, the transformation of product selectivity, the optimization of the HCOOH selectivity, activity and stability stem from the synergistic effect between metals and oxides in Ag-Sn during electrocatalysis. This research provides guidelines for the improvement of CO2RR selectivity by optimization of compositions and structures of Sn-based NPs.
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