【作者】 张涛；

【导师】 王国勇；

【作者基本信息】 吉林大学 ， 材料学， 2023， 硕士

【摘要】 化石燃料的大规模应用不仅会造成可预见的能源危机,还会导致大气中二氧化碳（CO₂）的浓度持续升高,打破自然界原有的碳循环过程,由此引发的一系列能源与气候问题会极大危害人类赖以生存的环境。当前,对CO₂进行收集、固定和再利用在我国为实现碳中和目标的背景下正受到越来越多的关注。其中,在可再生能源（太阳能、风能、水能等）的驱动下,电化学还原CO₂生成多种高附加值的化学产品具有良好的应用前景。然而,鉴于CO₂是热力学稳定分子且电化学还原CO₂反应面临电流密度低、产物选择性差等问题,设计合成出高效稳定的催化剂具有现实意义。作为贵金属,银已经被证实在CO₂还原反应中能表现出良好的催化活性和选择性,但储量少、价格昂贵等问题限制了其大规模的商业应用。铜基催化剂在多碳产物的生成上展现出良好的应用潜力。因此,以铜和银作为活性组分,构建复合材料,通过多组元组分间的协同作用能提高电催化还原CO₂性能。本论文主要以铜银二元复合材料为研究对象,通过成分和结构优化提高电化学还原CO₂性能并调控其还原产物的分布。具体的研究内容如下:1、本章合成了一系列Cu-Ag双相催化剂并保证了两相的晶粒尺寸相当。由于双相催化剂相尺寸呈单峰分布,因此可以通过调节元素比来控制相界面面积。研究发现,电化学还原CO₂为一氧化碳（CO）的催化性能随Cu-Ag催化剂界面面积的增加而单调增加,Cu₅₀Ag₅₀在-0.9 V的电位下对CO的选择性达到80.25%,CO的分电流密度为-4.88 m A cm^-2,且能保持10 h以上的催化活性,其催化性能甚至优于Ag₁₀₀。这是因为双相催化剂中Cu和Ag之间的电子效应和协同作用能降低催化反应中的动力学能垒。本章为降低电化学催化剂对贵金属的依赖提供了另一种途径。由于本研究的方法忽略了相的厚度,未来可以在减少贵金属元素的比例下进一步增大相界面。2、通过简单的湿化学法制备了s-Cu₂O（暴露（100）晶面）、d-Cu₂O（暴露（110）晶面）和As-Cu₂O（Ag纳米粒子修饰的s-Cu₂O）三种Cu₂O纳米颗粒,并研究了三种催化剂电化学还原CO₂制备乙烯（C₂H₄）的选择性和活性。结果表明As-Cu₂O有着最好的催化性能,在-1.1 V的电位下,C₂H₄的法拉第效率和分电流密度分别为32.46%和-5.21 m A cm^-2,此外,As-Cu₂O在12 h内具备良好的稳定性。对C₂H₄选择性和活性的提高可归因于纳米Ag粒子的修饰。一方面,Ag的加入能增加催化剂活性位点数量,减少Cu⁺还原为Cu⁰,降低催化反应过程的能垒。另一方面,Ag的加入也有助于*CO中间体的生成,从而促进后续催化剂上C-C偶联的发生。本工作为通过外源原子的引入进一步提高对C₂H₄的选择性和活性提供了新的方法和策略。更多还原

【Abstract】 The large-scale use of fossil will not only cause a foreseeable energy crisis,but also cause the concentration of carbon dioxide（CO₂）in the atmosphere to continue to rise,disrupting the natural carbon cycle.The resulting energy and climate problems will greatly harm the environment on which human live.At present,the collection,fixing and reusing of CO₂ are attracting more and more attention in the context of carbon neutrality.The electrochemical reduction of CO₂ to a variety of high value-added chemical products driven by renewable energy（solar energy,wind energy,water energy,etc.）has the application prospect.However,in view of the fact that CO₂ is a thermodynamically stable molecule and the electrochemical CO₂ reduction reaction faces the problems such as low current density and poor product selectivity,it is of practical significance to design the efficient and stable catalysts.As a precious metal,silver has been proved to show good catalytic activity and selectivity in CO₂ reduction reaction.However,its poor reserves and high price limit its large-scale commercial application.Copper-based catalysts show good application potential in the generation of carbon products.Therefore,when copper and silver were used as the active components to construct the composite,multi-component materials can improve the electrochemical CO₂ reduction performance through the synergistic interaction between components.This thesis mainly focuses on the copper-silver binary composite material,improving the electrochemical CO₂ reduction performance and regulating the distribution of reduction products through the composition and structure optimization.The specific research contents are as follows:1.A series of Cu-Ag biphasic catalysts were synthesized and ensured that the grain sizes of the two phases were equivalent.The phase interface area of the biphasic catalyst can be manipulated by the element ratio due to the unimodal phase size distribution.It is found that the catalytic performance of CO₂ electroreduction to CO is monotonically increased with the Cu-Ag interface area.A high Faradic efficiency of 80.25%was attained with a partial current density of-4.88 m A cm^-2 at-0.9 V vs RHE in Cu₅₀Ag₅₀and the FE_CO was almost not attenuated at the steady current density within 10 h.The catalytic performances are even better than those of Ag₁₀₀ catalyst.This is because the electronic effect and synergistic effect between Cu and Ag can effectively reduce the kinetic energy barrier in the catalytic reaction.The paper enlightens another way to reduce the dependence of electrochemical catalyst on noble metals.The phase interface can be further increased with less noble metal element proportion,for the methodology of this paper ignores the thickness of the phase.2.Three kinds of Cu₂O nanoparticles s-Cu₂O（exposed（100）crystal surface）,d-Cu₂O（exposed（110）crystal surface）and As-Cu₂O（s-Cu₂O modified by Ag nanoparticles）were prepared by a simple wet chemical method.And the selectivity and activity of electrochemical reduction of CO₂ to C₂H₄ by three catalyst electrodes were studied.The results indicate that As-Cu₂O shows the best catalytic performance,and the Faraday efficiency and partial current density of C₂H₄ are 32.46%and-5.21 m A cm^-2 at-1.1 V.In addition,As-Cu₂O has great stability within 12 h.The improvements of selectivity and activity of C₂H₄ can be attributed to the modification of Ag nanoparticles.On the one hand,the addition of Ag can increase the number of active sites,reduce the reduction of Cu⁺to Cu⁰,and decrease the energy barrier of catalytic reaction.On the other hand,the addition of Ag facilitates the formation of*CO intermediates,thus promoting the occurrence of C-C coupling on subsequent catalysts.This work provides a new method and strategy for further enhancing the selectivity and activity of C₂H₄ through the introduction of exogenous atoms.更多还原