热电子介导的CO2电化学还原机理研究

Electrochemical reduction of CO2 gas molecules is one of the promising ways to promote the global cycling of carbon and solve the greenhouse effect. While the reducing products include the energy molecules such as methanol, ethanol, methane in the case of the negative overpotential, especially the diversity of the intermediate and reduction product makes it a challenge to selectively control the reaction path. Herein, we proposed to choose the Cu-Pt, Cu-Au and Cu-Rh alloys which have different potentials for CO2 reduction as electrochemical electrodes. Especially nanoparticle-film configuration is introduced to enhance the plasmonic coupling within the nanoscale gaps, which can be tuned by depositing TiO2 insulating layers with different thicknesses. On the one hand, we investigate the molecular adsorption behavior in the strong near-field coupling in the case of distinct film thicknesses and laser wavelengths. On the other hand, we also investigate the excited state after hot electron injection condition and its influence to the subsequent reaction path. The exact energy and number of hot electron participating in the electrochemical reduction can be tuned by changing the near-field plasmonic coupling. Based on the dielectric polarization theory and molecular orbital theory, we try to reveal the effective way to lower both the reduction overpotential and reaction activation energy, as well as clarify electrochemical reduction mechanism of hot-electron mediated charge transfer and reaction selectivity. In compared with the randomly dispersed nanoparticles, hot electron behavior in the strong coupling conditions will provide theoretical guidance for designing Cu based electrochemical electrode with highly catalytic ability and high selectivity.

CO2气体分子的电化学还原是促进碳循环利用、解决温室效应的主要途径之一，然而只有在较负过电位下，才能生成甲醇、乙醇、甲烷等能源分子，中间产物和还原产物的多样性成为控制反应路径的难点。本项目拟选择具有不同过电位的Cu-Pt、Cu-Au和Cu-Rh合金作为电极，在Cu-TiO2基底上沉积分散的合金纳米粒子。一方面，通过改变TiO2薄膜的厚度、激光波长等参数来调节Cu基底与合金粒子之间的近场耦合，研究超强极化场下分子的吸附行为。另一方面，原位调节参与电化学还原的热电子能量和数量，研究热电子注入状态下分子的激发状态，以及其对反应激活能、反应路径的影响。最终拟从电介质极化理论、分子轨道理论出发，揭示降低还原过电位、降低反应激活能的有效途径，从而澄清热电子介导的界面电荷转移和选择性电化学还原机理。与分散纳米粒子相比，研究强耦合时的热电子行为将为设计高催化能力、高选择性的电极提供理论指导。

催化剂的电子态结构，几何参数、表面成分、孔道传质动力学行为等方面是影响分子活化、催化活性、催化动力学的重要因素。我们针对上述因素进行了深入的研究，并取得了以下成果:(1)化学法合成多孔金属壳层，激光激发表面等离激元，产生的热电子参与催化反应，促进分子极化，表现出优异的反应动力学。(2)脱合金法制备了多孔金-锡，银-铜和铜-铟催化电极，催化反应过够驱动银-铜电极发生表面重构，Cu偏析在电极表面，从而有效提高催化反应的稳定性和选择性。在纳米多孔铜-铟电极的催化过程中，也发现了类似的现象。通过对金-锡电极进行形态表征和元素分析发现，电极的高催化活性源于Sn原子固溶于Au晶格中所产生的拉伸应变。在CO2还原过程中，拉伸应变会导致中间产物*COOH在电极表面吸附能增加，提高催化选择性。(3)通过调节MoS2的缺陷密度，缺陷会束缚激子。研究O2在缺陷处的吸附行为，O2吸附可以增强荧光强度，其强度增加约3倍。总之，项目进展良好并且取得一些有价值的研究成果和重要进展。成果通过论文发表，人才培养的形式得以体现。项目执行期间，发表SCI论文9篇，其中5篇属于中科院JCR期刊1区。培养博士后2名，研究生5名，其中2名获博士学位，3名获硕士学位。其中2人获硕士国家奖学金，1人获博士国家奖学金。