【作者】 杨帆；

【导师】 夏宝玉；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2020， 博士

【摘要】 全球无限制的二氧化碳（CO₂）排放已造成严重的环境污染和气候变化等问题。电化学还原CO₂因其具有较高的还原效率和相对简单的实验环境,能够实现真正的碳元素循环,从而受到国内外学者的青睐。金属铜基材料是迄今为止最有可能实现高效转化CO₂为多碳烷烃类化合物的催化剂,但也面临产物选择性低和稳定性差等问题。本论文通过设计合成一系列的铜基催化剂,探究电化学CO₂还原催化性能和选择性的影响因素,以及研究电催化CO₂还原机理,从而获得具有高效催化CO₂制多碳类碳氢化合物的铜基催化剂。本论文主要研究内容如下:1.金属有机框架（MOFs）具有多孔结构可调的特点,利用反应物在混合溶剂中溶解度的差异合成不同形貌的Cu-乙酸腺嘌呤（Cu-ade）MOFs。其中阴极化还原的Cu-ade MOFs纳米片性能最好,烷烃的法拉第效率（FE）达到73%。在-1.4 V vs.RHE时乙烯（C₂H₄）的FE为45%,电流密度为8.5 m A cm^-2。而在-1.6 V vs.RHE时,甲烷（CH₄）的FE为50%,电流密度为15 m A cm^-2。研究表明,阴极化的Cu-ade MOFs重建形成的含氮配体的Cu纳米粒子有助于获得优异的CO₂转化性能。2.MOFs材料在电催化过程中不稳定,因此采用液液界面法制备纳米纤维状的Cu-天冬氨酸（Cu-ASP）MOFs材料,以此为前驱体,通过调控退火条件,调控材料的结晶状态和表面结构,形成多孔Cu O纳米线,并结合原位还原形成氧化物衍生的铜材料的策略,实现了高选择性还原CO₂生成C2产物（C₂H₄和CH₃CH₂OH）,在-1.3 V vs.RHE下,具有最高的C2产物FE,约为70%。Cu O衍生的Cu催化剂具有的优良活性和选择性主要与丰富界面的独特多孔结构有关,并且原位拉曼光谱表明金属Cu是CO₂电解的真正活性中心。3.利用液相还原法制备不同氧化状态的Cu催化剂（Cu⁰～Cu⁺）,探究不同氧化状态Cu催化剂对于电催化CO₂还原活性以及产物选择性的影响。实验结果表明,随着电压降低,高氧化状态的Cu₂O材料生成C₂H₄的FE逐渐降低,CH₄的FE相应增加。而低氧化状态的Cu催化剂在整个施加电位下有效抑制CH₄的产生,高效生成C₂H₄产物。合适氧化状态的Cu催化剂能够高效地将CO₂还原至C2（C₂H₄和CH₃CH₂OH）产物,最高FE达到74%,其中C₂H₄为主要产物,FE约为53%。4.合成Cu₂O纳米颗粒前驱体,利用离子交换法制备CuI材料,探究I^-阴离子对电催化CO₂还原活性以及产物选择性的影响。相比于Cu₂O,CuI材料具有高的电流密度,在整个施加电位下倾向于生成C2（C₂H₄和CH₃CH₂OH）产物。在-1.3 V vs.RHE下,C2产物的FE为53%左右。由于含有的I^-离子有助于形成并稳定产生C2物种的中间体,所以CuI催化剂有效地将CO₂转化为碳氢化合物。更多还原

【Abstract】 Global unlimited carbon dioxide（CO₂）emissions have caused serious environmental pollution and climate change.The electrochemical reduction of CO₂ is favored by scholars at home and abroad because of its higher reduction efficiency and relatively simple experimental environment so as to realize the real carbon cycle.Copper based materials are the most likely catalysts for the efficient conversion of CO₂ to hydrocarbons,but they also face the problems of poor product selectivity and stability.In this paper,a series of copper based materials were designed and synthesized to explore the factors influencing the catalytic performance and selectivity of CO₂ electrochemical reduction,as well as the research of catalytic mechanism,so as to obtain copper based catalysts with high efficiency of catalyzing CO₂ toward hydrocarbons.The main contents of this paper are as follows:1.Metal organic framework（MOFs）has the characteristics of porous and adjustable structure,based on the solubility difference of reactants in mixture solvents,Cu adenine MOFs（Cu-ade MOFs）with different morphologies were synthesized.The cathodized Cu-ade MOFs nanosheets demonstrate excellent catalytic performance for the CO₂ conversion into valuable hydrocarbon with a total hydrocarbon Faradaic efficiency（FE）of over 73%.Mainly,ethylene（C₂H₄）with a maximum FE of 45%is produced at-1.4 V vs.RHE with a current density of8.5 m A cm^-2,while methane（CH₄）demonstrates FE of 50%and current density of～15 m A cm^-2 at-1.6 V vs.RHE.These investigations reveal that the reconstruction of cathodized Cu^II/ade-MOF and the formed Cu nanoparticles functionalized by the nitrogen-containing ligands contribute to the excellent CO₂ conversion performance.2.The MOFs materials are unstable in the process of electrocatalysis,so the nanowires of Cu-ASP MOFs prepared by liquid-liquid interface method are used as the precursor.By adjusting the annealing conditions,the crystal state and surface structure of the materials are regulated,and combined with the strategy of in-situ reduction to form oxide derived copper materials,the high selective reduction of CO₂ to C2 products（C₂H₄ and C₃CH₂OH）is realized,the highest C2 product FE is about 70%at-1.3 V vs.RHE.The excellent activity and selectivity of cupric oxide nanowires is mainly relative to the unique porous structure with abundant interface.Moreover,the in-situ Raman spectra indicate that the metallic copper would be the real active sites for the CO₂ electrolysis.3.Various copper oxide with different oxidation states（Cu⁰～Cu⁺）was prepared via liquid phase reduction method,the effect of Cu catalysts with different oxidation states on the activity and selectivity of electrocatalytic reduction of CO₂ was investigated.For Cu₂O with high oxidation degree,with the decrease of voltage,the FE of C₂H₄ decreases and the FE of CH₄ increases.With the decrease of oxidation degree on Cu catalysts,CH₄ is largely suppressed and C₂H₄ definitely dominates at a wide potential window.Thus,the optimal oxidation state of copper can obtain high efficiency of C2 hydrocarbons（C₂H₄ and CH₃CH₂OH）.The highest FE of C2 hydrocarbons is 74%and the FE of C₂H₄ is about 53%.4.The CuI catalyst was synthesized using Cu₂O nanoparticles precursor by ion exchange method.The effect of anions on the activity and selectivity of electrocatalytic CO₂ reduction was investigated.Compared with Cu₂O,CuI has high current density and tend to produce C2（C₂H₄ and CH₃CH₂OH）products under the whole applied potential.The FE of C2 products is about 53%at-1.3 V vs.RHE.Because I ion in CuI catalyst helps to form and stabilize the intermediate of C2 species,thus effectively converting CO₂ into hydrocarbons.更多还原