硼掺杂多孔钯基催化剂的构筑及其电化学合成氨性能研究

Electrochemical ammonia synthesis is driven by the sustainable electricity using water as the hydrogen source, which is of significant importance for the sustainable development of the national economy. However, the low ammonia yield and faradaic efficiency of electrochemical ammonia synthesis greatly limits its industrial applications. In this project, we explore the preparation of boron-doped porous palladium-based catalysts with controllable composition and structure, and obtain catalysts with rich boron content, well-developed porous structure, excellent dispersibility and uniform particle size, and measure their performance for electrochemical ammonia synthesis. We plan to investigate the relationship among the morphology, composition, crystal structure, defects, alloying degree, specific surface area and catalytic performance of the catalysts, and reveal the crucial factors affecting the performance. Moreover, we employ the density functional theory to calculate the free energy of each step of the nitrogen reduction reaction, elucidate the adsorption/desorption, dissociation and bonding processes of nitrogen species on the catalyst surface, explore the structure change and charge distribution of catalyst surface during the nitrogen reduction reaction, and infer the rate determining step and catalytic mechanism of the nitrogen reduction reaction. Combination of theoretical and experimental results, we deduce and detect the intermediate species of nitrogen reduction reaction, and investigate the structure-activity relationship, reveal the synergistic interaction mechanism among metal, boron and nitrogen, and identify the type of active sites. The aim of this project is to provide experimental basis and theoretical guidance for the design, preparation and application of high-efficiency catalysts toward electrochemical ammonia synthesis.

电化学合成氨以水作为氢源，利用电能驱动氮气还原合成氨，对国民经济的可持续发展具有非常重要的意义，但是电化学合成氨存在产氨速率和法拉第效率低的问题。本项目拟探索组分和结构可控的硼掺杂多孔钯基催化剂的制备方法，获得富含硼掺杂、孔隙发达、分散性良好、粒径均匀的纳米催化剂，测试其电化学合成氨性能，研究催化剂的形貌、组成、晶体结构、缺陷、合金化程度、比表面积等因素与其催化性能的关系，揭示影响性能的关键因素。利用密度泛函理论计算催化剂氮还原反应基本步骤的自由能，阐明氮物种在催化剂表面的吸脱附、解离及成键过程，探讨氮还原反应过程中催化剂表面的结构变化和电荷分布，推断氮还原反应的决速步骤和催化机理。结合实验结果，推断并检测氮还原反应的中间过渡态，研究构效关系，揭示金属、硼与氮的协同作用机制，确定催化活性中心，为高效电化学合成氨催化剂的设计、制备和应用提供实验依据和理论指导。

氨作为重要的化工原料和能源载体，对国民经济的发展至关重要。传统哈伯-博施法合成氨需要高温高压的条件，从而消耗大量的化石燃料以及排放过量的温室气体。因此亟待开发清洁，低能耗，可持续的合成氨技术。电催化氮气还原反应是利用电能驱动氮气和水反应合成氨，对国民经济的可持续发展具有非常重要的意义。但是电催化氮还原合成氨存在氮气活化困难，竞争析氢反应强烈，导致产氨速率和法拉第效率低。为了解决这些难题，开发高活性，高选择性的催化剂是关键。虽然Pd已被证明是一种良好的氮还原反应的催化剂，但是其合成氨的性能还远达不到实际应用。为了进一步提高Pd基催化剂的活性和法拉第效率，形貌调控和组分改性是两种非常重要的方法。本项目开发了一种简便的方法构造了富含硼掺杂、孔隙发达的硼掺杂多孔钯基催化剂，研究催化剂的形貌、组成、晶体结构、缺陷、合金化程度等因素与其电催化氮还原合成氨性能的关系，阐明其构效关系。结果显示多孔结构能提高丰富的活性位点和快速的传质通道；硼掺杂不仅能提高氮吸附能力，而且在一定程度上抑制析氢反应的发生，从而提高合成氨的活性和法拉第效率。通过检测氮还原反应的中间产物，揭示金属、硼与氮的协同作用机制，推断氮还原反应的催化机理，确定催化活性中心，为高效电化学合成氨催化剂的设计、制备和应用提供实验依据和理论指导。因此该项目具有重要的科学意义和应用价值。