高指数晶面结构Bi单原子层电催化剂定向还原二氧化碳到甲酸的构效关系和机理研究

CO2 electrochemical reduction to liquid fuel and industrial chemicals with high value by renewable energy, such as solar energy, wind power, can improve the greenhouse effect. Since CO2R products are various and to achieve a directed synthesis is of difficulty, the study on how to obtain a kind of electrocatalyst with high selectivity and high activity becomes a research frontier. This project aims to modify the high-index faceted Pd nanocrystals by a surface modification to bring in a Bi atomic layer, with the realization of directional formate production during CO2R. The surface structure characteristics of Bi atomic layer modified Pd nanocrystals (including the Miller index of the crystalline planes, Bi/BiOx structure, Ag-Bi structure) and the structure-activity relationship of CO2R will be both systematically studied, through surface modification of Pd nanocrystals, the introduction of Ag or some other interesting atoms, and modification of Bi atomic layer structure. After that, the CO2R intermediates located in different wavebands will be detected by electrochemical in-situ vibrational spectroscopies with high sensitivity, including Infrared, Raman and Sum-Frequency Generation spectroscopies, respectively. Then, DFT theoretical calculations will be performed upon the results of electrochemical in-situ vibrational spectroscopies and the structure-activity relationship of CO2R. The mechanism of CO2R to formate at a molecular level will be finally revealed. Bi atomic layer modified Pd nanocrystal should possess a high catalytic activity result from the high-index faceted structure of Pd nanocrystals and from the unique electronic and geometric structure of the atomic layer, and also should have a high selectivity of formate production thanks to Bi. This project is expected to provide new ideas for the design and fabrication of a new kind of CO2R to formate electrocatalyst with high selectivity and high activity.

CO2电化学还原（CO2R）到液体燃料和高值化工原料，可以减缓环境压力，利用可再生能源。CO2R具有多种产物，提高催化剂的选择性实现定向合成极具挑战性，成为该领域的研究前沿。本项目拟制备高指数晶面结构Pd纳米晶，通过表面修饰形成Bi单原子层电催化剂，实现定向CO2R到甲酸液体燃料。通过改变Pd纳米晶的表面结构，掺入Ag等其他元素，调控Bi单原子层的结构，系统研究结构特征(晶面结构，Bi/BiOx结构，Ag-Bi结构)与电催化性能的构效规律。同时，运用红外、拉曼与和频光谱三种优势互补的电化学原位振动光谱，高灵敏地检测位于不同波段的CO2R中间体，结合DFT理论计算，从分子水平揭示Bi单原子层定向催化CO2到甲酸的机理。本项目的研究集成了高指数晶面结构催化剂的高活性、单原子层独特的电子和几何结构、Bi电催化CO2产甲酸高选择性，有望为CO2R产甲酸的高活性和高选择性新型电催剂的设计提供新思路。

电化学CO2还原为将CO2转化为高附加值燃料和工业原料提供了一种有前景的策略。在设计和研究电催化剂以获得碳氢化合物方面虽然取得了重大突破，但该反应仍受到反应产物选择性差和活性低的限制。在已开发和使用的电催化剂中，铋基催化剂是CO2还原过程中产甲酸性能最优的材料之一。然而，铋基催化剂在催化过程中对于产甲酸的过电位过高以及电流密度偏低，限制了其广泛的应用。Bi覆盖度为50%时具有最大的电流密度，约为-0.19 mA cm-2，对应的产甲酸法拉第效率为44.71%，要优于其他Bi覆盖度。对比50%覆盖度的产甲酸法拉第效率（44.71%）要优于满单层的产甲酸法拉第效率（28.46%），表明Pd产生的*H对Bi吸附的CO2分子具有加氢作用。高指数Pd纳米晶载体具有最高的产甲酸法拉第效率，是低指数Pd纳米晶载体的2倍左右，表明高指数晶面Bi能促进CO2还原产甲酸。 基于金属有机框架，在氩气氛围下600°煅烧制备了BiAg双金属（BiAg-600）纳米催化剂。BiAg-600为核壳结构，壳层为富Bi，内核是BiAg分相。相比Bi-600，BiAg-600的产甲酸法拉第效率最高，约97%对应的产甲酸盐偏电流密度为58.6 mA cm-2，甲酸盐产率为974 μmol cm-1 h-1。在流动池测试中，BiAg-600表现出工业级的稳定电流，在200mA cm-2的电流密下具有的产甲酸法拉第效率为94.3%。采用电化学原位衰减全反射红外谱和电化学原位壳层分离金纳米颗粒增强拉曼光谱，结合同位素示踪技术，确认HCO3-不仅仅是pH缓冲液，是CO2从电解质向催化剂表面转移的媒介。BiAg-600上的CO2还原是一个串联反应：在Ag位点上，通过HCO3-的连续消耗和再生（或迁移）模式捕获CO2分子，捕获的CO2*接受CO2*•-的第一个电子，然后在Bi位点上进一步加氢还原为*OCHO-。本项目对深入认识CO2在Bi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Nature Communications等期刊上共发表包括3篇标注项目号的SCI论文，指导在读硕士研究生1名。