场致效应增强二氧化碳还原及其反应机理研究

Fossil fuels are currently the major energy source and are rapidly consumed to supply the increasing energy demands of mankind. Carbon dioxide (CO2), an inevitable product of fossil fuel combustion, leads to possible climate change and may pose a serious impact on our environment. There is an increasing need to mitigate CO2 emissions using carbon-neutral energy sources. The electrochemical reduction of CO2 (CO2RR) offers a compelling route to energy storage and high-value chemical manufacture. It enables the use of increasingly abundant renewable energy sources, such as solar and wind, to drive the conversion of CO2 to renewable fuels and feedstocks. Despite recent breakthroughs, the energy efficiency of CO2RR is still far from being a viable alternative to fossil energy sources. Improvements in both selectivity and activity of CO2RR at low overpotential are of crucial importance to continue the advance in the direction of commercial viability.. Recently, we reported that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO2 close to the active CO2 reduction reaction surface. This result points to field-induced reagent concentration (FIRC) as a means of enhancing CO2RR appreciably. Unfortunately, this effect has been only demonstrated in CO2RR to single-carbon products reduction. Here, we would like to extend FIRC to more challenging CO2RR to multi-carbon productions, such as ethylene, ethanol, et al. To this end, we will optimize the local electric field by controllable preparation of metal and metal alloy nano needles. Then, the electronic structure of the nano needle surface and interface will be well modified by atomic layer deposition to reach high activity and selectivity of CO2RR to multi-carbon productions. The atomic and electronic structures of the materials and their surface and interface will be fully investigated using in-situ X-ray absorption spectroscopy. Finally, we will use in-situ Raman and in-situ FTIR to study the CO2RR process and the key intermediates, paving an avenue to reach the real CO2RR mechanism. These knowledge will provide guidelines for high efficient catalyst design and preparation for high efficiency CO2RR to multi-carbon products and accelerate its practical applications.

随着社会的发展，能源危机日益严重，与此同时，二氧化碳排放量亦逐年增加，这些对人们的生存造成了严重威胁。采用电催化方法还原二氧化碳，可以在比较温和的条件一步直接获得一氧化碳、乙烯和乙醇等高值化学品和液体燃料。同时，该过程与可再生能源或富余核能利用相结合，实现大规模电能存储，表现出极具潜力的应用前景，已成为相关领域一个重要的研究热点。我们将围绕新近发现的金属纳米针尖引起的催化反应新机制——场致反应物浓度机制，通过制备金属纳米针尖及其复合物，实现对局域电场的调控及金属纳米针尖表界面的调控，通过原位同步辐射X射线吸收光谱探索二氧化碳还原与材料电子结构的构效关系，并通过原位拉曼光谱和原位红外光谱对二氧化碳还原过程和关键中间物产生及转变过程进行研究，揭示二氧化碳还原真实过程及机理，为高效催化剂设计及制备提供理论指导，实现CO2还原到多碳产物，如乙烯、乙醇等，效率和选择性的提高，推进二氧化碳工业进程。

电催化CO2还原技术因其温和的反应条件可被认为是解决当前能源问题和温室效应的有效途径。新近研究发现，纳米针尖引起的场致反应物浓度机制可以有效增强CO2还原性能，是一种极有潜力的调控策略。通过调控局域电场和针尖表界面，利用X射线吸收光谱和原位表征技术研究CO2还原与材料电子结构的构效关系，揭示CO2还原反应机理。我们获得了以下系列成果：（1）通过调控表面曲率，实现局部电场增强有效促进了Cu催化剂对 C2产物的选择性。（2）构建有序纳米针尖阵列结构可以大大增强局域电场，催化剂为CoS2时可以促进碱性条件下的电化学析氢性能。（3）类似纳米针尖阵列结构，催化剂为Ag时可以抑制HER，促进CO2还原。（4）类似纳米针尖阵列结构，催化剂为Cu时提升表面K离子浓度，有利于*CO吸附，提升对C2产物的选择性。（5）通过铜纳米针包覆聚四氟乙烯实现局部电-热场的协同增强，提高*CO中间体和促进C−C耦合从而高效转换二氧化碳为C2产物。（6）Ag催化剂表面Sn杂原子诱导的局域电场增强了对*COOH的吸附，有利于CO2还原为CO。