催化学报 ›› 2016, Vol. 37 ›› Issue (7): 1081-1088.DOI: 10.1016/S1872-2067(15)61048-8

• 论文 • 上一篇    下一篇

高选择性和稳定性SnO2纳米催化剂上CO2电化学还原为甲酸

付奕舒a, 李亚楠a, 张霞a, 刘予宇b,c, 周晓东d, 乔锦丽a   

  1. a. 东华大学环境科学与工程学院, 上海 201620, 中国;
    b. 太原理工大学环境科学与工程学院, 山西 太原 030024, 中国;
    c. 东北大学大学院环境科学研究科, 仙台 980-8579, 日本;
    d. 南卡罗来纳大学化学工程系, 哥伦比亚, 南卡罗来纳州 29208, 美国
  • 收稿日期:2015-12-18 修回日期:2016-01-27 出版日期:2016-06-17 发布日期:2016-06-17
  • 通讯作者: Yuyu liu, Jinli Qiao
  • 基金资助:

    上海市教育委员会科研创新项目(14ZZ074);上海市科学技术委员会"科技创新行动计划"国际学术合作交流项目(14520721900);东华大学研究生创新基金(15D311304);东华大学国家环境保护纺织工业污染防治工程技术中心项目.

Electrochemical CO2 reduction to formic acid on crystalline SnO2 nanosphere catalyst with high selectivity and stability

Yishu Fua, Yanan Lia, Xia Zhanga, Yuyu liub,c, Xiaodong Zhoud, Jinli Qiaoa   

  1. a. College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China;
    b. College of Environmental Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China;
    c. Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan;
    d. Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA
  • Received:2015-12-18 Revised:2016-01-27 Online:2016-06-17 Published:2016-06-17
  • Contact: Yuyu liu, Jinli Qiao
  • Supported by:

    This work was supported by the Innovation Program of the Shanghai Municipal Education Commission (14ZZ074), the International Academic Cooperation and Exchange Program of Shanghai Science and Technology Committee (14520721900), Graduate Innovation Fund of Donghua University (15D311304) and the College of Environmental Science and Engineering, State Environmental Protection Engineering Center for Pollution Treatment and Control in Textile Industry, Donghua University. All the financial supports are gratefully acknowledged.

摘要:

作为最重要的还原产品,甲酸是CO2还原中非常有价值的液体燃料.已有研究报道,Sn类金属电极对甲酸生成有很好的催化活性,所用电解液均为KHCO3溶液(0.5mol/L),但多数研究没有对其电解液条件的影响给出清晰解释.一般而言,电解液pH值会影响H2O和CO2还原的电极电势,酸性环境有利于氢析出,碱性环境则不利于甲酸形成.在中性偏碱性环境,CO2电解可以提供维持氧化物稳定性的可能性.同时,电解质浓度也极大地影响甲酸形成.研究表明,当在固定床反应器中使用Sn颗粒电极,在KHCO3溶液(0.5mol/L)中甲酸的法拉第效率比K2CO3溶液(0.1mol/L)的法拉第效率更大.我们研究组通过简单的水热自组装法成功制备了一种纳米结构SnO2催化剂.其中SnO2-50纳米催化剂由三维多级结构组成,为纳米颗粒和微米球的聚集体,其中含有直径为500nm-1μm的高度多孔结构.该催化剂负载气体扩散电极用于CO2电化学还原,表现出优异的CO2还原催化活性和甲酸选择性.与其他文献报道相比,该电极具有明显的低过电位(-0.56Vvs.SHE).经研究发现,这与甲酸形成由传质和电荷传递过程控制有关,同时CO2还原强烈依赖于电解液条件.此外,催化剂的电化学性能和甲酸选择性强烈依赖于电解液浓度.在0.5mol/LKHCO3电解液中,当电解液浓度为0.1-0.5mol/L时,催化性能随电解液浓度增加而提高,同时在电解液浓度为0.5mol/L时催化性能达到最佳,获得56%的甲酸法拉第效率,这主要是由于HCO3-直接参与反应的结果.在电解液浓度较低时,甲酸的形成由传质控制,而在电解液浓度较高时,甲酸的形成则由电荷传递控制.同时我们发现在形成甲酸过程中,电解液pH值对CO2电化学还原过程有很大影响.为了研究电解液pH值影响,重点考察了pH值分别为6,7,8.3和9时的电位值,其原因是酸性过高有利于氢气形成,碱度过高不利于甲酸形成.结果表明,pH=8.3的电解液为CO2还原的最佳电解液条件.此外,在最负的电势下,电解液pH=8.3时,阴极电流密度比其他电解液都大,几乎是pH=6的电解液的2倍.此时在中性偏碱性环境下,CO2还原可以提供维持氧化物稳定性的可能性.当电解液pH增加到9.0时,甲酸产量及法拉第效率略有下降,可能是碱性环境不利于甲酸形成.同时,对SnO2-50纳米催化剂经28h电解后的甲酸法拉第效率的衰减机制进行了深入研究.结果表明,随着电解时间延长,甲酸法拉第效率衰减.电解时间为1-28h时,法拉第效率和甲酸产量均保持平稳下降趋势,28h后法拉第效率由初始的56%降至24%.有文献报道,甲酸法拉第效率随电解时间的改变主要是由于阳极上甲酸的氧化或阴极上杂质的污染.为了证明阴极电解后的状态,我们对SnO2-50/GDL阴极电解前后的XPS谱进行了分析.结果发现,法拉第效率的下降是由于痕量氟离子沉积到SnO2-50/GDL电极表面,这些痕量氟离子可能来自反应槽,阻碍电极表面CO2电化学还原为甲酸.

关键词: 二氧化碳还原, 二氧化锡, 甲酸, 法拉第效率

Abstract:

A novel catalyst for CO2 electroreduction based on nanostructured SnO2 was synthesized using a facile hydrothermal self-assembly method. The electrochemical activity showed that the catalyst gave outstanding catalytic activity and selectivity in CO2 electroreduction. The catalytic activity and formate selectivity depended strongly on the electrolyte conditions. A high faradaic efficiency, i.e., 56%, was achieved for formate formation in KHCO3 (0.5 mol/L). This is attributed to control of formate production by mass and charge transfer processes. Electrolysis experiments using SnO2-50/GDE (an SnO2-based gas-diffusion electrode, where 50 indicates the 50% ethanol content of the electrolyte) as the catalyst, showed that the electrolyte pH also affected CO2 reduction. The optimum electrolyte pH for obtaining a high faradaic efficiency for formate production was 8.3. This is mainly because a neutral or mildly alkaline environment maintains the oxide stability. The faradaic efficiency for formate production declined with time. X-ray photoelectron spectroscopy showed that this is the result of deposition of trace amounts of fluoride ions on the SnO2-50/GDE surface, which hinders reduction of CO2 to formate.

Key words: Carbon dioxide reduction, Tin dioxide, Formate, Faradaic efficiency