產物的選擇性一直是二氧化碳電化學還原觸媒所面臨的問題。在眾多種類電化學觸媒中，二氧化錫相較於其他金屬與金屬氧化物觸媒具有低成本、製備簡單與產氫過電位較高的優點，而在中性電解液中二氧化錫觸媒上二氧化碳還原所能生成的產物有甲酸根與一氧化碳。其中一氧化碳因為可與氫氣生成經濟價值較高的甲醇、分離容易且過電位較低而具有優勢，因此本研究欲探討如何提高二氧化錫對於一氧化碳的產物選擇性。
本研究主要分為兩個部分: 第一部分為探討不同的水熱合成參數及不同電解電位對於二氧化錫上二氧化碳還原產物選擇性的影響，並試著找出最佳化參數以得到最高的一氧化碳產率與選擇性。結果顯示在較正電位下，降低晶粒大小能夠提高一氧化碳之選擇性。另外，本研究也根據X射線吸收光譜(XAS)以及X射線電子能譜儀(XPS)之實驗結果嘗試提出二氧化碳在二氧化錫上的還原反應途經。第二部分則是藉由在二氧化錫中加入二氧化鈦達成進一步降低晶粒大小的目標。透過水熱法所製備類似內核-外殼結構之二氧化錫-金紅石相二氧化鈦觸媒在-0.86 V(RHE)電位下，其一氧化碳產率可提高至42%，一氧化碳選擇性也能夠進一步提高至二氧化錫觸媒之兩倍。

Product selectivity is a challenge in the electrochemical reduction of CO2. Among various catalysts, tin oxide is one of the hottest catalysts for the electrochemical reduction of CO2 due to its low cost, easy synthesis and high hydrogen evolution overpotential. Moreover, carbon monoxide and formate are the only two products of CO2 reduction when tin oxide is employed, which can be easily separated by the solubility in water. In this thesis, a new way is demonstrated to increase the yield and selectivity of carbon monoxide in the electrochemical reduction of CO2 since carbon monoxide and hydrogen are synthesis gas for methanol production, which show a high economic value.
In the first part of this thesis, the relation between synthesis parameters and the selectivity of CO under different applied potentials is investigated. The result shows that under less negative potentials, reducing the crystal size of SnO2 leads to increase the CO selectivity. The reduction pathways of CO2 on SnO2 based on the X-ray adsorption spectroscopy and x-ray photoelectron spectroscopy data are reasonably proposed. In the second part, the crystal size of SnO2 is further reduced by the synthesis of the core-shell-like SnO2-rutile TiO2 catalysts through the hydrothermal method. A relatively high Faradaic efficiency over 42% for the CO formation and two folds of CO selectivity in comparison with the case using the SnO2 catalyst can be achieved at -0.86 V (RHE).

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