离子液体氢键强化超临界CO2光电转化新机理及新过程

The desirable advantages of ionic liquids such as high conductivity and wide electrochemical window have made them exceptional solvents for photoelectrochemical reduction of CO2. But the larger viscosity of the ionic liquid limits its application. Supercritical CO2 has characteristics such as low viscosity and high diffusivity, but it is not conductive.The combination of the two solvents can greatly increase the solubility of CO2 in ionic liquids, reduce the viscosity of ionic liquids, improve the mass transfer and heat transfer efficiency of ionic liquids.After the reaction, supercritical CO2 can be used to extract the organic products dissolved in ionic liquids without cross-contamination.This project studies the photoelectrochemical reduction of CO2 in supercritical CO2/ionic liquid two-phase system. The regulation law of photoelectrochemical reduction of CO2 by ionic liquids under supercritical conditions was obtained.Through theoretical calculation, dynamic simulation combined with in situ characterization techniques, the interaction of the hydrogen bonding between ionic liquids and CO2 under supercritical conditions will be studied.The mechanism of photoelectrochemical activation of CO2 intensified by ionic hydrogen bonding under supercritical conditions will be revealed to further improve the conversion efficiency and selectivity.The photoelectric synergistic effect under supercritical conditions will be researched and solar-driven CO2 photoelectric reduction system will be achieved. This project will open the way for the high utilization of CO2 and will be of importance to address environmental pollution and energy source shortage in our country.

离子液体具有电导率高、电化学窗口宽等优势成为光电还原CO2的理想溶剂，但离子液体较大的粘度限制了其应用。超临界CO2具有低粘度、高扩散性等特性，但本身不导电。两者的结合可以极大地增加CO2在离子液体中的溶解度，降低离子液体的粘度，提高离子液体的传质、传热效率，反应完成后还可以利用超临界CO2把溶解在离子液体中的有机产物萃取出来而不产生交叉污染。本项目拟通过超临界CO2/离子液体两相体系中光电还原CO2的研究，获得超临界条件下离子液体对CO2光电还原的调控规律；通过理论计算、动力学模拟结合原位表征技术，研究超临界条件下离子液体与CO2的氢键相互作用，揭示离子液体氢键强化的CO2光电催化活化机制，为进一步提高CO2光电转化效率提供科学依据；研究超临界条件下光电协同效应，实现太阳能驱动的CO2光电还原系统。该项目为CO2的高值利用开辟了途径，对解决我国环境污染和能源问题具有重大意义。

光电还原CO2利用太阳能将CO2转化为高附加值产品是实现“碳中和”的有效途径之一。针对目前光电转换效率低、还原产物选择性差等问题，本研究制备了具有较大比表面积、较高表面活性位点、较高原子利用率以及较快电荷分离特性的单原子层Co3O4、Co1-xS、C负载单原子Bi和铜、氮共掺杂碳纳米管（Cu-N-CNT）等光电催化材料，以离子液体为电解液，进行了光电催化还原CO2研究。考察催化材料、光、电、外加偏压、离子液体结构等对光电催化还原CO2反应的产物分布、产率和选择性的影响规律，其中Cu-N-CNT显示了优异的电催化还原效率并可实现CO高选择性。在离子液体电解液中，Cu-N-CNT在很宽的过电位范围内（0.32V 到0.62 V）保持CO法拉第效率大于90%，在0.52V过电势时CO法拉第效率达到最大值96.3%，该过电势低于以KHCO3水溶液为电解液时的过电势（0.63 V）。同时，CO法拉第效率最大时对应的CO分电流密度为22.6 mA cm-2，大于在KHCO3水溶液电解质中的CO分电流密度。表明离子液体电解液不仅可降低电催化还原CO2制CO的过电势，还明显提高了电催化活性。在宽电位范围内保持高法拉第效率不仅能够提高产物的生成速率，还可使催化剂适用于大规模电催化还原装置，对于CO2电催化还原的工业化应用具有十分重要的意义。同时理论计算表明，Cu-N3-C是活性更高的催化位点，在此活性位点上，CO2还原的能垒更低，有利于反应的发生，并且其d带电子中心更靠近费米能级，更易于反应中间体的稳定，成功实现了CO2的高效电催化转化。该研究为CO2的循环利用和太阳能的转化和储存提供科学依据，对解决我国环境污染和能源短缺、实现双碳目标具有重大意义。