离子液体功能化硼单原子催化剂的设计制备及其电催化NRR机理研究

Electrochemical nitrogen reduction reaction (NRR) to produce ammonia at room temperature and ambient pressure has high energy efficiency, and it is a promising method for ammonia synthesis. The major challenges for NRR are the low catalytic activity in traditional catalysts, as well as the low N2 solubility and the competing hydrogen evolution reaction (HER) in aqueous electrolytes, which result in low current efficiency and low ammonia yield rate. To overcome the above barriers, we propose a novel approach of catalysts design with high catalytic activity and high selectivity, which essentially requires the introduction of functional group into single atom (SA) catalysts from the structure of ionic liquids, which show high N2 solubility and the ability of effective suppression of HER. With combination of the advantages of ionic liquids with sing-atom catalysts, which has shown high selectivity and activity in electrochemical reactions, it is supposed to enhance the interaction with N2 and promote the NRR efficiency. The proposed project will focus on a) fundamentally understanding of the interactions between the functional groups and N2 molecular and the NRR intermediates; b) mechanistic design of functional group modified graphene with high capture capacity of N2; c) design of functional boron/graphene single-atom catalysts and investigation of the synergetic catalysis mechanism for NRR. This project will develop ionic liquid functionalized graphene supported boron single atom catalysts with high selectivity and catalytic activity for NRR progress. The development of the proposed ionic liquid functionalized single atom catalysts will open a new window for the design of electrochemical NRR system for ammonia synthesis.

电催化氮气还原（NRR）合成氨可在常温常压条件下进行，能量利用率高，是最近极受关注和极具发展潜力的新型合成氨路线。但目前催化剂活性低、水溶液中析氢竞争反应（HER）显著，极大限制了电流效率（FE）和合成氨速率的提高。本项目拟开展具有高N2溶解度并可有效抑制HER的离子液体功能基团的研究，明确其结构特征及其与N2、NRR反应中间物的相互作用机理；研究离子液体功能基团化学修饰石墨烯的基团结构和分布状态对N2捕获、活化和NRR反应路径的影响规律；结合催化剂结构分析和DFT理论计算，建立硼单原子/功能化石墨烯协同催化提高NRR效率的机理和模型。基于上述研究成果，耦合离子液体和单原子催化剂的优势，研制离子液体功能化石墨烯负载的硼单原子催化剂，建立高选择性、高活性催化体系的NRR合成氨技术，为高效电催化合成氨提供理论依据。

电催化氮气还原（NRR）可在低温低压条件下合成氨，能量利用率高，是极具发展潜力的合成氨新路线。然而由于传统催化剂活性低，并且水溶液体系N2溶解度低、HER副反应占主导地位，导致目前电流效率（FE）和合成氨速率低。针对该问题，本项目主要开展了离子液体功能基团-含氟基团改性石墨烯、硼掺杂材料和过渡金属催化剂的设计、制备及合成氨性能研究，并结合理论计算，开展了其催化机理的探索。考察了含氟基团对N2 吸附的影响规律，建立了含氟基团改性硼掺杂石墨烯催化剂协同催化提高NRR效率的机理和模型。基于理论计算模型，制备了氟硅烷改性硼掺杂石墨烯新型催化剂，提高了氮气还原的电流效率和合成氨速率，NRR的电流转化效率达到9.8%，合成氨速率≥1×10-10 mol·s-1·cm-2。此外，通过采用硝酸盐作为原料开展合成氨研究，制备了高效的Ru/Ni复合催化剂，合成氨的电流效率接近100%，合成氨速率>10-6 mol·s-1 cm-2，超过美国能源局设定的合成氨目标。进一步，本项目开发了一种利用金属-硝酸盐电池体系将硝酸盐废水转化为氨的电池系统。该电池系统以活泼金属如镁、铝、锌、锂及其合金为电池阳极，以镍基，钌基或铜基催化剂为阴极，含硝酸盐废水作为电解质，电池发电的同时将废水中的硝酸盐转化为氨。通过将Ru/Ni复合催化剂电极与锌箔组装燃料电池，能够输出电功率高达51.5 mW cm-2 (0.25 cm2 电极面积) 或者 23.3 mW cm-2(1 cm2电极面积)，同时在40 mA cm-2的电流密度长时间运行条件下，能够维持硝酸盐转化氨的电流法拉第效率高达97.4%。本研究对于丰富氮气还原催化剂材料的设计和制备，提高合成氨效率，揭示合成氨催化反应本质具有重要意义。