基于质子导体氧化物载体的CO2加氢反应电化学增强催化原位表征及机理研究

Synthesizing liquid fuels through electrochemical hydrogenation of CO2 is a practical way in efficient using renewable energy while reducing greenhouse gas emission. A metal supported on an ionic conductor has an effect, called as electrochemical promotion of catalysis (EPOC), on many reactions. However, the catalyzing mechanism is still not clear. In this project, we are going to use an ionic-conductor-supported Fe or Cu, metals of which possess special electronic structure, as the cathode catalyst. In situ characterization of Raman, XRD, and STM/STS, etc., will be applied to investigate the hydrogenation process of CO2 on the cathode catalyst, in a temperature range of 300-450C. The purpose is to figure out the correlation of electronic state, chemical composition, intermediate species, structure, and defects of the surface or interface of the catalyst to the environmental factors such as temperature, partial pressure of gases, and electrical potential of the cathode. Therefore, combining theoretical modeling and simulation as well as some ex situ characterization, we are going to find out the reaction route, the rate-controlling step, and the key intermediate species which determine the overall selectivity of the hydrogenation of CO2 on the cathode. Meanwhile, we will study the effect of proton from different sources on the catalyzing behavior, though comparing two reaction modes, i.e., a mode of solid oxide cell (SOC, in which only CO2 is the reactant at cathode and the hydrogen source is provided by the proton coming across the proton-conducting electrolyte) and a mode of electrical promotion of catalysis (EPOC, CO2 and H2 are co-provided to cathode). Through the implementation of this project, a new investigation method based on in situ characterization and a novel mechanism of EPOC will be proposed and established.

通过电化学方式将CO2加氢制备液态燃料是充分利用可再生能源和减少温室气体排放的有效途径。以离子导体为载体的金属对很多反应呈现出电化学增强催化（EPOC）效应，但其机理还不清楚。本项目以质子导体氧化物BZCY7担载具有特征电子结构的铁和铜作为阴极催化剂，采用拉曼、XRD、扫描隧道谱等原位表征手段，在300-450C温度范围，对CO2在阴极催化剂上的加氢过程进行测试分析，以获取催化剂表界面的电子态、成分及中间产物、结构及缺陷等与温度、气氛、电极电势等环境因素的关联信息，进而结合理论计算和离线测试，探明CO2加氢反应的途径、速控步、决定选择性的关键中间产物；同时，通过对比电池反应模式（SOC：阴极反应气体仅为CO2，氢源来自电解质传递过来的质子）和电化学增强模式（EPOC，反应气为CO2和H2的混合），研究不同质子来源对催化的影响。拟通过项目的实施，建立一套原位表征新方法，提出EPOC新机制。

固体氧化物电池（SOC）由传导氧离子或质子的氧化物电解质及其两侧的多孔电极构成。传统意义上的SOC主要用于发电（SOFC）和电解（SOEC）。通过本项目的实施，将SOC发展成一种高温电化学反应器并关注其电极催化反应产物，该研究正在逐步成为催化领域的一个新分支。本项目重点研究了质子导体材料及其构成的反应器对CO2的电化学加氢和电解水性能；探讨了基于氧离子导体的碳和甲烷的高温电化学氧化以及水和CO2的高温电解性能。取得的重要进展包括：（1）研究了掺钇的锆酸钡和铈酸钡系列质子导体材料的烧结特性及其在H2O和CO2中的稳定性，通过优化的Fe和Ni掺杂改善了电解质的性能，制备的管式SOFC在600C的峰值功率密度达465 mW cm-2；温度低至200C时，也测到了1.3 mW cm-2的输出。（2）采用氧离子导体YSZ电解质、Ag-GDC正极和Ni-YSZ负极组装反应器，实现了CH4和CO2的同步电化学氧化和还原，获得合成气产物；对反应器各种能量损失来源的分析，表明了同步电化学氧化还原与分别进行CO2的电解和CH4的电化学氧化相比的优越性，其在槽电压0.9 V时，800C的运行电流密度可达1 A cm-2。（3）基于氧离子导体反应器的阳极可实现CO的电化学氧化、产生的CO2可通过逆向Boudouard反应将固体碳气化生成CO的原理，研制的平板式和管式直接碳SOFC，均实现了大于10 W的输出。利用CO2的吸收剂CaO，实现了全密封碳-空气电池的运行，其放电能量密度达1300 Wh kg-1。（4）基于质子导体电解质的SOEC，在氧电极用空气带入50%水蒸气，700C、1.3V时的电解电流密度达 1.8 A cm-2，稳定测试了90小时。（5）将Mn-Na2WO4/SiO2催化剂置于管式SOFC内部并通入甲烷，以氧离子的形式向甲烷供氧，对甲烷的电化学氧化偶联进行的初步探讨。