【作者】 张旭；

【导师】 马天翼；

【作者基本信息】 辽宁大学 ， 化学工程（专业学位）， 2020， 硕士

【摘要】 自从Fritz Haber在1909年用氮气和氢气合成氨气以来,合成氨工业就被认为是20世纪最伟大的化学发明。因为合成氨反应的重要意义和巨大的挑战性,使得这一反应在工业应用以及基础理论研究领域都被重点的关注和研究。目前,工业上利用Haber-Bosch反应在高温高压条件下合成氨,不仅消耗大量能源,并会导致环境污染和温室气体排放,随着地球能源日益枯竭和环境污染严重,当前迫切需要探索一种更加高效环保的合成氨方法。通过电化学还原氮气合成NH₃/NH₄⁺是一种更加经济环保的合成氨方法,这一过程在常温常压下即可发生,大大节省了能源消耗;设备简单易操作,相比于Haber-Bosch反应,可以大大地节省设备和操作费用;原料氮气和水在地球上有丰富的储量,而且简单易得;反应所需电能可以从风能、太阳能等可持续能源转换得到。凭借这些优点,使电化学催化合成氨受到广泛关注。在本文中,我们采用安瓿法制备电化学合成氨的催化电极材料。将反应的原材料装入安瓿瓶内,安瓿瓶被抽真空后,它的开口端通过热熔化密封然后进行加热反应来合成所需材料。真空密封的安瓿瓶消除了环境的影响,使前驱体反应物充分反应,通过控制反应物的质量比,可以控制产物形态和电荷状态等,由此产生电催化性能。安瓿法因其对反应条件和环境的可控性,为电催化剂的可控合成提供了一个新的途径。本文首先采用安瓿法,以廉价的不锈钢箔为基底和硫粉在真空环境下高温煅烧生成FeS₂催化电极,该电极材料表面具有丰富的缺陷和硫空位,以及FeS₂晶面之间的协同作用,使其具有良好的电催化性能,在常温常压下,在酸性0.1M Li₂SO₄电解质溶液中,-0.2V vs.RHE时,法拉第效率高达14.6%,产率可达11.5μg h^-1mg_Fe^-1;通过电化学测试发现,FeS₂催化电极可以有效抑制析氢反应的发生,从而具有良好的选择性;此外,由于电极材料中Cr的存在,该电极在酸性电解液条件下具有长期稳定的催化性能。因此,以不锈钢为基底的FeS₂电极在电催化合成氨领域具有巨大的潜力。另外,采用相同的方法,以丰富廉价的Zn箔为基底和硫脲在真空环境下高温煅烧合成ZnS₂催化电极,通过材料表征发现,该电极材料具有丰富的表面缺陷,此外,由于反应过程中有N元素的参与,使得材料表面具有大量的N空位,增强了电极表面对N₂的吸附性,从而使该催化电极具有良好的电催化性能,常温常压下,在碱性0.1M KOH电解质溶液中,-0.5V vs.RHE时,法拉第效率高达19.067%,-0.6V vs.RHE时产率可达3.2μg h^-11 cm^-1;该催化电极只有在在碱性电解质溶液中,才能保持良好的稳定性,而且碱性条件也减弱了析氢反应,从而有利于电催化合成氨反应的进行。更多还原

【Abstract】 Ever since Fritz Haber synthesized ammonia with nitrogen and hydrogen in1909,the ammonia industry has been considered the greatest chemical invention of the 20th century.Because of the significance and great challenge of ammonia synthesis reaction,this reaction has been widely concerned and studied in both basic theory research and practical industrial application.At present,the ammonia is synthesized by the Haber-Bosch reaction under high temperature and high pressure conditions,it not only consumes a large amount of energy,but also leads to environmental pollution and greenhouse gas emissions.With the shortage of the earth energy and serious environmental pollution,it is urgent to explore a more efficient and environmentally friendly synthetic ammonia method.It is a more economical and environmentally friendly method of synthesizing ammonia by electrochemical reduction of nitrogen to synthesize NH₃/NH₄⁺,which can occur at room temperature and atmospheric pressure,and greatly saves energy consumption;compared with Haber-Bosch reaction,its equipment is simple and easy to operate,and could greatly save the cost of equipment and operating;The raw materials nitrogen and water have abundant reserves on the earth and they are easy to obtain;Electric energy can be obtained from sustainable energy conversion such as wind and solar energy.By virtue of these advantages,electrochemical NH₃ production has received widespread attention.Here,we use ampoule method to prepare catalytic electrode materials for electrochemical ammonia synthesis.The raw materials of the reaction were loaded into the ampoule bottle,after the ampoule bottle was vacuumed,its opening end is sealed by hot melt and then heated to react to synthesize the required material.The vacuum sealed ampoule bottle eliminates the influence of the environment and makes the precursor reactants fully react.By controlling the mass ratio of the reactants,the product morphology and charge state can be controlled,resulting in electrocatalytic performance.The ampoule method provides a new way for controllable synthesis of electrocatalysts because of its controllability to reaction conditions and environment.Firstly,The stainless-steel-based catalytic electrodes were obtained by a facile one-step sulfurization of stainless-steel foil with sulfurpowder in a vacuum sealed ampoule calcined at high temperature.The surface of the electrode material is rich in defects and sulfur vacancies,as well as the synergy between the crystal planes of FeS₂,which make it have outstanding electrocatalytic performance;Under room temperature and pressure,in the acidic 0.1M Li₂SO₄ electrolyte solution,at-0.2V vs.RHE,the Faraday efficiency is as high as 14.6%,and the yield of NH₃ is 11.5μg h^-1mg^-1Fe;Electrochemical measurements showed that FeS₂ catalytic electrode could effectively inhibit the hydrogen evolution reaction and thus have good selectivity.In addition,due to the presence of Cr in the electrode material,the electrode has long-term stable catalytic performance under acidic electrolyte conditions.Therefore,the FeS₂ electrode based on stainless steel has great potential in the field of electrocatalytic ammonia synthesis.In addition,using the same method,the Zn-based catalytic electrodes were obtained by a facile one-step sulfurization of rich and cheap Zn foil with sulfocarbamide in a vacuum sealed ampoule calcined at high temperature.Through the material characterization,it was found that the electrode material has rich surface defects.Morever,due to the participation of N in the reaction process,the surface of the material has a large number of N vacancies,which enhances the adsorption of N₂ on the electrode surface,so that the catalytic electrode has outstanding electrocatalytic performance.Under room temperature and pressure,in the alkaline 0.1M KOH electrolyte solution,at-0.5V vs.RHE,the Faraday efficiency is 19.067%,and the yield of NH₃ is 3.2μg h^-1cm^-1 at-0.6V vs.RHE.The catalytic electrode can maintain stability only in the alkaline electrolyte solution,and the alkaline conditions also weaken the hydrogen evolution reaction,which is beneficial to the progress of the electrocatalytic ammonia synthesis reaction.更多还原