SOEC阴极原位脱溶纳米Ru催化常压合成氨气及机理研究

Industrially, ammonia is synthesized at intermediate temperature and high pressure, the operation condition is strict. It is of great significance to realize the synthesis of ammonia at atmospheric pressure by electrochemical method. In this project, using in-situ exsolved nano Ru particles modified LSCrF as the cathode, GDC as a solid electrolyte, a SOEC reactor will be assembled for electrochemical synthesis of ammonia at intermediate temperature and atmospheric pressure. The relationship between cathodic composition and the crystal structure parameters will be investigated to design cathode material. The dominant phase diagram of in-situ exsolved reaction of the cathodic material was studied from calculated and measured thermodynamics parameters. Based on deep analyzing the mechanism of in-situ exsolved reaction, nano-Ru catalytic layer will be prepared on the surface of SOEC cathode. Its effects on microstructure, properties of cathode and ammonia synthesis efficiency will be investigated. The effects of applied electric field, working temperature and gas partial pressure on the ammonia synthesis efficiency will be also studied to optimize the operation condition. The oxidative-reduction, oxygen transport behavior of nano Ru modified cathode material will be researched, as well as the adsorption and desorption behavior for the reaction gas, then the mechanism of promoting the cathodic catalytic reaction by surface modification will be studied. The relation equation between electric field strength, temperature, nitrogen and hydrogen partial pressure and ammonia synthesis efficiency will be established. The above study will provide the theoretical basis for in-situ exsolve modified cathode materials and electrochemical synthesis of ammonia at intermediate temperature and atmospheric pressure using nitrogen and water vapor as raw materials.

工业上合成氨需要在中温高压下进行，反应条件苛刻，通过电化学实现常压下氨的合成具有重大的研究意义。本项目以原位脱溶纳米Ru改性的LSCrF作为阴极，GDC作为固体电解质组成SOEC反应器中温常压下电化学合成氨。通过研究阴极组分和晶体结构参数的关系，设计阴极材料；计算和测量阴极材料的部分热力学参数，研究阴极材料脱溶反应的优势区相图，深入分析脱溶的反应机制，制备SOEC阴极表面纳米Ru催化层；研究催化层对阴极结构、性能和氨合成效率的影响规律；研究外加电场、工作温度、气体分压对氨合成效率的影响，优化合成工艺；研究纳米Ru改性阴极材料的氧化-还原行为、氧传输行为，及材料对反应气体的吸脱附行为，分析表面改性促进阴极催化反应的机理；建立电场强度、温度、氮气和水蒸气分压与氨合成率的关系方程。通过上述研究，为原位脱溶改性阴极材料和以氮气、水蒸气为原料中温常压下电化学合成氨气提供理论依据。

本项目以固体氧化物电解池（SOEC）的阴极为研究对象，通过原位脱溶纳米金属粒子表面改性的方法来提高阴极的电导率和电催化活性，进而提高SOEC常压下电化学合成氨的速率。.首先采用高温固相反应合成制备了La0.33Sr0.67CrxFe1-xO3-δ（LSCrF）阴极粉体。在对阴极组分设计进行了优化的基础上复合Ce0.8Gd0.2O2-δ（GDC），并通过原位脱溶的方法成功制备出Ru纳米粒子修饰的LSCrF-GDC阴极，Ru纳米粒子为球形，颗粒在5nm左右。 .研究了阴极厚度、微观结构以及阴极组分对电极极化阻抗的影响规律，结果表明当x=0.67，阴极厚度为20.75μm，使用聚甲基丙烯酸甲酯（PMMA，5μm）作为造孔剂时，LSCrF-GDC电极的极化阻抗最小，700℃时为4.025Ωcm2。在研究的温度范围内（600-800℃），Ru纳米粒子修饰后阴极的极化阻抗显著降低，700℃的极化阻抗为3.495Ωcm2，下降了13.17%。 .以N2和H2O为原料，通过LSCrF-GDC/GDC/BCFN-GDC单电解池实现了常压下电化学合成氨，研究了温度、电压对合成氨速率的影响。在研究的400-750℃范围内，氨的合成速率随着温度升高先增大后减小，电压升高，氨的合成速率增大，但过高的电压会降低电池稳定性，减少电池寿命。550℃，1.6V电压条件下，以LSCrF-GDC为阴极氨的合成速率可以达到2.37×10E-10mols-1cm-2；Ru纳米粒子修饰后LSCrF-GDC阴极后，在相同电压和温度条件下，电池的电流密度提高，氨合成速率相应提高，550 ℃可达到4.73×10E-10mols-1cm-2，提高了99.58%。.Ru纳米粒子在材料表面析出增加了电极表面的活性位点，同时晶体中产生更多的氧空位，有利于氧离子的表面吸附和体传输，产生更多的氢离子参与氨合成反应。Ru纳米粒子修饰的LSCrF-GDC阴极粉体表面碱活性位点增多，有利于N2的解离吸附，也促进了氨合成反应的进行。