包覆型Fe-M (M=Ru, Mo)合金材料的制备及电催化氮还原机理研究

Catalytic synthesis of ammonia is a pillar of the huge chemical industry. However, mature industrialized nitrogen fixation requires harsh condition and is of high energy consumption and dangerous. Therefore, it is of crucial importance to explore nitrogen fixation technology under normal temperature and pressure and mild conditions in order to figure out a novel approach to reduce the energy consumption and cost of the present ammonia synthetic technique. Electrocatalytic synthesis of ammonia is becoming one of the research areas which receives extensive attention due to the fact that driven by electric energy, it assists the activation of nitrogen molecule and fixation. Nevertheless, the key limitation for its development is the lower current efficiency and conversion percentage as a result of the difficulty in catalyzing adsorption and activation of nitrogen molecule with electrocatalysts. Thus, exploration of a class of potential effective nitrogen reduction electrocatalyst is considerably important. This project attempts to draw on Fe, Ru or Mo acting the most efficient catalytic active center in terms of synthesis of ammonia, and to take a two-step approach along with synthetic technology optimization for the preparation of high index facets of Fe-based alloy nanomaterials as nitrogen reduction electrocatalysts with superior activity and stability. Theoretical calculation is used to establish rational models and to estimate possible intermediate species, thereby elucidating electrocatalytic nitrogen activation modes and reaction mechanism. This project is instructive both experimentally and theoretically for the research and application of efficient nitrogen fixation electrocatalysts as well as deep understanding of their electrocatalytic mechanism; it thus advances promising application of electrochemical synthesis of ammonia.

催化合成氨是一个庞大的化学支柱产业，而成熟的工业固氮条件苛刻、能耗大且危险。因此，探索常温常压条件下的固氮工艺至关重要。其中，电催化氮还原反应是在温和条件下，利用电能来实现氮分子的活化和固定，因而成为备受关注的研究领域之一，但制约其发展的关键是N2在电催化剂表面的吸附和活化较困难，导致氮固定的产率及法拉第效率较低，因此探索一类潜在的高效氮还原电催化剂极为重要。本项目试图借鉴Fe, Mo, Ru为固氮有效的催化活性成分，采用两步法，优化合成工艺，制备高活性、高稳定性的碳包覆型Fe-M (M=Ru, Mo)基合金纳米材料作为电催化氮还原电催化剂。运用理论计算手段，建立合理结构模型，预测可能存在的反应中间物种，阐明电催化氮活化方式及反应机理。本项目的开展为高效电催化氮还原反应电催化剂的研究、应用及深入理解其电催化机制提供一定的实验与理论指导，进而拓展了电化学合成氨潜在的应用前景。

氨气 (NH3) 是一种清洁的非碳基新能源液体燃料，可以高效的储存氢能，其体积能量密度是液氢的1.5倍，具有能量密度高、易于传输等优点，可以作为未来能源经济中氢的替代品。而成熟的工业固氮条件苛刻、能耗大且危险。因此，探索常温常压条件下的固氮工艺至关重要。其中，电催化氮还原反应是在温和条件下，利用电能来实现氮分子的活化和固定，因而成为备受关注的研究领域之一。然而，氮气是一种非极性惰性气体，且在水中溶解性极低，导致其在电催化剂表面及附近的浓度较低，以及负电位下氮气还原面临着析氢反应的竞争问题，导致其产氨量和法拉第效率都很低。加之目前对该反应机理缺乏深刻的理解，很难实现有的放矢地理性设计新型的氮还原电催化剂。本项目实施过程中一方面通过构建仿生位点，提高电催化固氮产率；一方面通过表面修饰策略改变材料表面的亲疏水性质，这样不仅可以提高催化剂表面及附近氮气浓度，更重要的是可以一定程度上抑制析氢反应，进而提高电催化固氮的法拉第效率。同时，运用理论计算手段，阐明了其电催化氮活化方式及反应机理。本项目的开展为高效电催化氮还原反应电催化剂的研究、应用及深入理解其电催化机制提供一定的实验与理论指导，进而拓展了电化学合成氨潜在的应用前景。