【作者】 赵金虎；

【导师】 贾法龙； 张礼知；

【作者基本信息】 华中师范大学 ， 物理化学， 2012， 硕士

【摘要】 随着经济的发展和自然资源的消耗,空气中CO2的浓度逐渐增加,从而产生了“温室效应”。为了解决温室效应对人类的生存环境和可持续发展产生的负面影响,将CO2转化为可用的有机化合物提供了一个具有可行性的方法。近年来将CO2通过电化学还原转化成碳氢化合物,特别是具有高能量密度的醇类产物,引起了国际科学工作者的关注。目前的研究表明在所有的金属电极材料中,铜电极催化CO2生成醇类产物的法拉第效率最高,主要是由于其具有适当的析氢过电位、弱的CO吸附能力以及催化CO发生进一步还原的特殊性质。而纳米多孔铜电极由于其特殊的纳米结构及更高的比表面积,它在CO2电化学还原中有可能表现出特殊的催化活性。本论文具体的研究内容分为以下几个方面：1,我们开发了简易的合金/电化学去合金化方法制备多孔铜电极,主要过程是首先在铜表面电沉积一层锌,然后通过热处理直接在铜表面形成合金层,最后利用电化学去合金化的方法溶出锌组分而得到多孔铜。我们探讨了热处理温度、去合金方法、电解质等因素对孔结构的影响。结果显示,150℃下热处理1小时的Cu-Zn样品在25mM盐酸溶液中用电位扫描的去合金化方法可以得到有序的多孔结构。2,针对CO2电还原体系中醇类产物(甲醇和乙醇)的精确定量检测,我们尝试了顶空-固相微萃取法和静态顶空法等分析方法,最终建立了液体进样-气相色谱检测的有效测试方法。主要通过离子交换树脂法除去溶液中的盐类,然后将处理后液体样品直接注入气相色谱中检测。此方法操作简便而且具有较好的重现性,为定量比较不同条件下CO2还原醇类产物的法拉第效率提供了保障。3,我们分析了电解质种类及还原电压对还原产物(甲醇和乙醇)法拉第效率的影响,结果表明碳酸氢钾水溶液最适合CO2向醇类产物的电化学转化,在-1.1V时醇类产物的法拉第效率最高。4,我们将制备的多孔铜用于CO2的电催化还原,结果表明多孔铜催化CO2向醇转化的效果要低于光滑铜。原因是由于去合金化过程中有少量的锌残留在多孔铜中,降低了铜的催化活性。实验发现不同的铜材料经过合金/去合金化后得到的多孔铜中锌的残留量有差别,锌的残留量越多,醇类产物的法拉第效率越低。为了解决这一问题,我们通过电沉积的方法在多孔铜表面负载上一层纯铜而又不至于堵塞多孔结构,从而提高了醇类产物的法拉第效率。更多还原

【Abstract】 With the development of economy and consumption of natural resources, the concentration of CO2in the air is gradually increased, leading to the "greenhouse effect". To solve the negative influence of greenhouse effect on living environment and sustainable development, conversion of CO2to usable organic compounds provides a feasible solution. In recent year, the scientists in the world paid more attention to the electrochemical reduction of CO2to hydrocarbons, especially the alcohols with high energy density. Present research results showed that the CO2could be reduced into alcohols with highest Faradic efficiency on the copper electrode among all the metal materials. The reason is that copper electrode possesses medium hydrogen overvoltage, weak CO adsorption and special catalytic property to convert CO to more reduced species. With the special nanostructure and much higher surface area, the nanoporous copper electrode could exhibit special catalytic activity towards the electrochemical reduction of CO2.The content of this paper is divided into the following aspects:1. A convenient alloy/electrochemical dealloying method was developed to synthesize porous copper electrode. The corresponding fabrication process was performed by electro-deposition of Zn on Cu, heat treatment to form alloy, and electrochemical dealloying to strip the Zn component. We investigated the effects of thermal treatment temperature, dealloying process, electrolyte and other factors on the pores’structure. The results showed that ordered porous structure could be formed by thermal-treatment of Zn-Cu sample at150℃for1h and subsequent electrochemical dealloying through potential scanning in25mM hydrochloric acid solution.2. To meet the accurate requirement of quantitative detection of the products of CO2electrochemical reduction, we tried different methods such as the headspace-solid phase micro extraction and static headspace. Finally, an effective measurement system was established through the liquid injection-gas chromatography method. This method was mainly involved with the removal of salts in solution by ions exchange resin, and direct injection of treated solution into the gas chromatography for measurement. This method was convenient and reproducible, and provided an insurance for quantitative comparison of faradic efficiency of alcohols in the reduced products prepared under different conditions.3. We analyzed the influence of the electrolyte species and the reduction potential on the faraday efficiency for the reduction products (methanol and ethanol). The results indicated that potassium bicarbonate aqueous solution was most suitable for the electrochemical conversion of CO2to alcohol products. The Faraday efficiency of the alcohol product reached the highest at-1. Ⅳ.4. We used prepared porous copper for the electrocatalytic reduction of CO2, and the results showed that the efficiency of the porous copper for CO2conversion is lower than the smooth copper. The reason was that there were small amount of zinc left in the porous copper during the alloying process, and reduced the catalytic activity of copper. It was found that residual zinc amounts in porous copper was not same if different copper materials were treated after the alloy/dealloying process. The more the zinc amounts left, the lower Faraday efficiency of the alcohol products was. To solve this problem, a thin layer of pure copper was electrodeposited on the surface of the porous copper without blocking the block the porous structure. As a result, the Faraday efficiency of the alcohol products was improved.更多还原