高指数晶面结构Cu纳米晶的制备与CO2电催化还原性能研究

Electrocatalytic reduction of CO2 is a hot topic in interdiscipline of electrochemistry, environmental science and energy science. Cu is a unique electrocatalyst for CO2 reduction, only which can convert CO2 into a series of organic molecules, such as hydrocarbons, alcohols and carboxylic acid. However, there are still several open questions: 1) Surface structure of Cu nanocatalyst is not well defined; 2) Catalytic activity and selectivity of Cu catalyst still need to be improved further; 3) The reaction mechanism of CO2 reduction, especially how C-C coupling to form C2+ products is not clear. It has been demonstrated that bulk high-index planes of Cu (e.g., Cu(711) and Cu(610)) have high electrocatalytic activity for CO2 reduction, and high selectivity for C2+ products. In this project, we want to take our advantages in high-index faceted Pt-group metal nanocrystals, electrocatalysis, and spectroelectrochemistry, to prepare Cu nanocrystals bounded by tunable high-index facets (such as tetrahexahedron and trapezohedron) to improve the electrocatalytic activity and selectivity for CO2 reduction. We then try to use a series of electrochemical in situ spectroscopic methods including FTIR, Raman and SFG to monitor reaction surface process and intermediates, as well as GC-MS, HPLC and electrochemical online MS and NMR to analyze reaction selectivity. We want to combine these results with DFT theoretical calculation to reveal CO2 reduction mechanism on Cu surfaces. This project may provide high-index faceted Cu nanocrystals with high catalytic performance for CO2 reduction, and help to elucidate the relationship between surface structure and catalytic activity for CO2 reduction.

CO2电催化还原是当前电化学、环境科学和能源科学等学科交叉的研究热点。Cu是该反应的一个特殊的电催化剂，只有它能够把CO2还原成碳氢化合物、醇和羧酸等有机物，但存在着Cu纳米催化剂结构不明确、催化活性和选择性不高、反应机理不清楚的关键问题。本体Cu的高指数晶面对CO2还原具有高催化活性和高C2以上产物的选择性。本项目拟在现有贵金属高指数晶面结构纳米晶的研究基础上，发展非贵金属纳米晶的电化学控制合成技术，制备由不同高指数晶面围成的Cu纳米晶（如二十四面体、偏方三八面体等），显著提高对CO2电催化还原的活性和选择性。在此结构明确的Cu纳米晶上，综合运用多种优势互补的电化学谱学方法（红外、拉曼、和频、质谱、核磁共振等）和色谱技术，检测CO2电还原过程的吸附态反应中间体和产物分布，并结合DFT理论计算，阐明构效规律和反应机理。

CO2电催化还原是当前电化学、环境科学和能源科学等学科交叉的研究热点。Cu是该反应的一个特殊的电催化剂，只有它能够把CO2还原成碳氢化合物、醇和羧酸等有机物，但存在着Cu纳米催化剂结构不明确、催化活性和选择性不高、反应机理不清楚等问题。本项目中我们结合金属纳米催化剂表面结构可控制备与理论计算，着重研究了不同表面结构的Cu基催化剂，特别是高指数晶面结构纳米晶对CO2电催化还原的性能与反应机理。取得如下主要结果：1）成功制备出了{530}高指数晶面结构的Cu二十四面体；2）首次制备出晶面连续可调的高指数晶面结构Pd二十四面体，并作为模型催化剂，获取构效规律，有效填补了传统本体单晶面模型催化剂与实际纳米催化剂在结构和尺度上的鸿沟；3）高指数晶面结构Pd二十四面体表面修饰Cu，有效调控了CO2电催化还原的反应选择性，发现单层Cu修饰时主要液相产物为乙醇，其选择性随着台阶原子的密度增加而增加，在{730}表面上法拉第效率可达27%。而0.8层Cu修饰时液相产物主要为甲醇。结合理论计算解释了反应选择性随Cu的覆盖度而变化的规律。DFT理论计算表明相较于纯Cu和纯Pd，在Pd台阶位上的单层Cu原子具有比较合适的CO吸附能（比Cu强，比Pd弱），使得CO2更容易发生还原，也有利于C-C偶联生成乙醇；4）通过制备铜基合金催化剂、还原氧化铜(OD-Cu)表面修饰、具有CO2捕获能力的碳载体材料等，调控了CO2还原的选择性；5）运用从头算分子动力学模拟等理论计算，证明Cu(100)表面CO2还原为CH4是按质子-电子转移机理，明确了溶剂水和界面电荷对CO2还原的促进机制。本项目对深入认识CO2在Cu基催化剂上电化学还原的选择性调控、构效规律和反应机理具有重要意义。项目执行期间在J. Am. Chem. Soc., Chem. Commun., ACS Catal.等期刊上共发表包括25篇标注项目号的SCI论文，指导5名硕士研究生毕业，协助指导3名博士研究生毕业，博士后出站一人。