【作者】 张蕊；

【导师】 张锦秋；

【作者基本信息】 哈尔滨工业大学 ， 化学工程（专业学位）， 2020， 硕士

【摘要】 在电催化CO₂还原反应中,金属铜是唯一一种能将CO₂转化为多碳产物的金属催化剂。但是铜的CO₂电还原产物种类繁多且选择性较低。制备氧化物衍生铜催化剂是一种通过调控铜催化剂的纳米结构来提高产物选择性的有效方法。在流动池中使用无粘结剂的铜纳米线催化剂,可以改善CO₂传质、避免活性位点被粘结剂覆盖,对于提高铜催化剂的选择性和催化活性具有重要意义。本文确定了在以5,5-二甲基乙内酰脲（DMH）为配位剂的镀液体系中电沉积铜,通过湿法氧化法将铜转化为Cu O,再利用恒电势还原法将Cu O还原为铜纳米线。较好的Cu O电还原条件是电解液为0.1 mol?L-1 KOH和还原电势为-0.8V（vs.RHE）。比较了H型电解池和流动池中电沉积铜前驱体制备的铜纳米线电还原CO₂的选择性,发现流动池中使用1 mol?L-1 KOH为电解液时,电沉积铜前驱体制备的铜纳米线对乙烯的选择性较高,为22%。对电沉积铜的工艺进行了优化,p H为8.5,镀液温度为45℃,电流密度为2 A?dm-2时在疏水碳纸上恒电流沉积得到的铜作为催化剂的前驱体较好,在-0.8V（vs.RHE）时实现对乙烯最高的选择性38%。通过恒电流电沉积法,在铜离子和锌离子摩尔浓度比为95:5的DMH镀液体系中,在疏水碳纸上电沉积了铜锌合金作为制备铜纳米线的前驱体。铜锌合金在形成纳米线的过程中锌溶解,容易生成更多的缺陷,如晶界或空位。对比了p H为9.0,镀液温度为25℃,电流密度为2 A?dm-2时电沉积得到的铜、铜锌合金及2种衍生纳米线的催化性能。对乙烯的选择性由大到小的顺序是:铜锌合金衍生的铜纳米线>铜衍生的铜纳米线>铜锌合金>铜。相对于金属铜衍生的铜纳米线,铜锌合金衍生的铜纳米线对乙烯的选择性增加到30%。基于密度泛函理论（DFT）模拟计算了多种中间产物在块铜、铜纳米线、带顶空位的铜纳米线和带侧空位的铜纳米线上的吸附能,研究了空位对H吸附、H活化、水分解反应和乙烯生成反应路径的影响,解释了上述结构不同的铜催化剂在性能上存在差异的原因。计算表明,铜纳米线中顶空位的存在会增大催化剂的活性,降低生成CO的相对能量,同时增大了CO在催化剂表面的吸附能,最终表现为乙烯选择性的提高。更多还原

【Abstract】 In the electrocatalytic CO₂ reduction reaction,metallic copper is the only metal catalyst that can convert CO₂ to multi-carbon products.However,there are many types of copper CO₂ electroreduction products and the product selectivity is relatively low.The preparation of oxide-derived copper catalyst is an effective method to improve product selectivity by adjusting the nanostructure of copper catalyst.Using the binderless copper nanowires catalyst in the flow cell can improve mass transfer of CO₂ and prevent the active site from being covered by the binder,which is of great significance for improving the selectivity and catalytic activity of the copper catalyst.First of all,this paper optimizes the process of electrodepositing copper and determines that in the plating solution system with 5,5-dimethylhydantoin（DMH）as the complexing agent.The copper was converted to Cu O by wet oxidation,and then the Cu O is reduced to copper nanowires by potentiostatic reduction method.The better conditions for Cu O electroreduction are that the electrolyte is 0.1 mol·L-1 KOH and the reduction potential is-0.8V（vs.RHE）.The selectivity of copper nanowires prepared by electrodepositing copper precursors in the H-type cell and the flow cell was compared for the electroreduction of CO₂.The copper nanowires have a higher selectivity to ethylene,22%.The process of electrodepositing copper is optimized.When the p H is 8.5,the bath temperature is 45°C,and the current density is 2 A?dm-2,copper obtained by constant current deposition on hydrophobic carbon paper is better as a catalyst precursor.The highest selectivity to ethylene is 38% at-0.8V（vs.RHE）.By a constant current electrodeposition method,a copper-zinc alloy was electrodeposited on a hydrophobic carbon paper as a precursor for preparing copper nanowires in a DMH plating solution system in which the molar concentration ratio of copper ions and zinc ions was 95:5.Zinc of the copper and zinc alloy was dissolved during the formation of nanowires,and are prone to generate more defects,such as grain boundaries or vacancies.The catalytic performance of copper,copper-zinc alloy and two derived nanowires obtained by electrodeposition at p H 9.0,plating bath temperature of 25℃ and current density of 2 A?dm-2 was compared.The order of selectivity to ethylene is as follows: copper-zinc alloy-derived copper nanowires>copper-derived copper nanowires>copper-zinc alloy>copper.Relative to metallic copper-derived copper nanowires,the selectivity of copper-zinc alloy-derived copper nanowires to ethylene has increased to 30%.Finally,based on the density functional theory（DFT）simulation,the adsorption energy of various intermediate products on bulk copper,copper nanowires,copper nanowires with top vacancies and copper nanowires with side vacancies was calculated.The effect of vacancies on H adsorption,H activation,water decomposition reaction and ethylene formation reaction path explain the difference in performance of copper catalysts with different structures mentioned above.Calculations show that the presence of top vacancies in the copper nanowires will increase the activity of the catalyst,reduce the relative energy for generating CO,and at the same time increase the adsorption energy of CO on the surface of the catalyst.Eventually,the selectivity of ethylene will increase.更多还原