纳米合金与有机催化剂修饰碳电极催化CO2电还原合成甲醇/乙烯的研究

The direct electrochemical reduction of CO2 to versatile chemicals methanol/ethylene has attracted more and more attention. Although quite good progress has been made in this area, some challenges and drawbacks still exist such as the use of noble metal electrodes or readily deactivation Cu electrode, low selectivity, low yield and low current efficiency for the target product (methanol or ethylene). To overcome these drawbacks, we will be devoted to developing a highly efficient and stable electrode catalytic system, which can effectively catalyze the multi-electron reduction of CO2 for the selective synthesis of methanol or ethylene. In our investigations, the readily available carbon-based materials (carbon fibers, graphite or carbon nanotubes) will be used as the electrode (cathode) and modified with nanoalloys and/or organic catalysts (such as pyridinium derivatives). The catalytic activity and stability of the carbon-based electrode could be greatly improved by control over the components，surface microstructures (morphology and grain size) and specific surface area of the electrode, and with the assistance of the synergistic effect of different metals or the co-effect between nanometals and organic catalysts. The detailed reaction mechanism will be fully investigated by cyclic voltammetry experiments and theoretical computations of quantum chemistry. The mechanistic insights should aid understanding side-reactions and developing more efficient electrocatalysts for the reduction of CO2 to the desired product. In addition, the competition reaction of hydrogen evolution and other side-reactions at the cathode should be prohibited or avoided via the optimization of electrocatalysts and electrolytic conditions. Our goal is that the carbon-based electrode modified by nanoalloys and/or organic catalysts could replace noble metals as the cathode for the electrocatalytic reduction of CO2, to afford the target product methanol or ethylene in a high selectivity, excellent yield and high current efficiency. It is expected that our investigations could provide a new and highly efficient electrochemical route (electrocatalytic system) for the conversion and utilization of CO2.

本项目以二氧化碳直接电还原转化为高附加值的化工产品甲醇/乙烯为研究对象，拟采用易得的碳基材料（碳纤维、石墨、碳纳米管等）为阴极，以具有独特催化活性的纳米合金、有机催化剂（如吡啶衍生物）修饰碳基电极，通过调控电极表面的组成、微观形貌结构、比表面等，并利用不同金属或纳米金属与有机催化剂之间的协同催化作用，研制出高效、稳定、低成本的碳基电极催化体系，替代贵金属电极或纯铜基电极，高效异相催化CO2电还原选择性合成甲醇/乙烯，探索发展具有实际应用价值的电还原CO2的新方法、新技术。借助循环伏安实验和量子化学理论计算，深入地研究CO2 电还原反应机理，弄清电极失活及副产物形成的原因，优化电极催化体系和CO2电还原条件，抑制析氢还原竞争反应和其它副反应，以期得到高产率、高选择性、高电流效率的目标产物甲醇或乙烯，从而解决制约着CO2电还原转化利用的关键问题，为CO2的有效转化利用奠定坚实的基础。

在该项目研究中，我们课题组应用电化学沉积法、阳极氧化法和水热合成法分别制备了Ni-Cu纳米合金与有机氮化合物修饰碳电极、铟-锡纳米合金 In-Sn修饰碳纸纤维电极 GDE-InxSn1-x、纳米氧化铋修饰玻碳电极、具有介孔结构的锡基电极Sn/SnOx等电极催化剂体系，用于电催化还原CO2，在隔膜电解池中，把CO2直接转化为有价值的化工产品（如甲酸、甲醇等）。我们的研究结果揭示：1）电极催化剂的催化活性、稳定性与电极的组成、表面的微观结构和形貌、晶体结构等密切相关；2）In-Sn纳米合金修饰碳纸纤维电极 GDE-In0.9Sn0.10优于纯In或纯Sn金属电极和其它GDE-InxSn1-x电极；3）具有纳米颗粒结构的Bi2O3催化活性明显优于纳米细棒结构的Bi2O3修饰玻碳电极；4）具有介孔结构的锡基电极Sn/SnOx的电化学活性表面积是普通的Sn箔电极的8倍，催化活性高于单纯的Sn金属电极，表面氧化物（SnOx）层也有助于提高电催化还原CO2的活性；5）Ni-Cu纳米合金与有机氮化合物共同修饰碳电极优于Ni-Cu纳米合金单独修饰碳电极。通过该项目的研究，我们成功地开发出高效、稳定的电极催化剂体系（如In-Sn纳米合金修饰碳纤维电极GDE-In0.9Sn0.10、纳米Bi2O3修饰玻碳电极、具有介孔结构的锡基电极Sn/SnOx等），电催化还原CO2生成甲酸法拉第效率可达90%以上，连续电解22小时催化活性能维持稳定，解决了催化剂活性低、稳定性差等关键问题，显示出良好的应用前景。另外，我们以CO2为C1原料，替代有毒的CO或光气，首次由CO2、芳基肼和多聚甲醛（醛）合成具有药物活性的含氮杂环1,3,4-噁二唑-2（3H）酮衍生物；也首次以CO2、胺和酮为原料合成氨基甲酸烷基酯类化合物，发展了合成这二类化合物的新方法，研究结果发表在国际主流刊物上并获得授权发明专利，拥有自主的知识产权，为二氧化碳的转化利用拓展了具有潜在应用价值的新途径。