三维多孔低配位金属单原子碳基催化剂的构筑及氮还原合成氨性能研究

Electrochemical synthesis of ammonia with zero carbon emission is essential to break the limitation of fossil fuels and develop low-carbon economy. To achieve its industrial practicability， it is important to modulate the active center of nitrogen reduction reaction electrocatalyst to improve current efficiency of electrochemical synthesis of ammonia. Researches indicate that the low coordination number (<4) of metal binding with nitrogen atoms in carbon-based catalysts with atomically dispersed M-Nx active sites is beneficial for enhancing the current efficiency of nitrogen reduction reaction. Nevertheless, there is a huge challenge for the rational fabrication of the catalysts with atomic-dispersed low low-coordinated M-Nx (X<4) active sites. Based on the above understandings, herein, we proposed the strategy to construct the atomic-dispersed low-coordinated M-Nx active sites via a "top-down" process of atoms migration, in which the metal atoms in large particles generating at high temperature migrate to the simultaneously fabricated structural basis with multiple edge sites constructed by urea. Moreover, taking advantage of template simultaneously, the three-dimensional porous carbon-based catalysts with atomically dispersed low-coordinated metal atoms could be controllably obtained, effectively exposing the low-coordinated M-Nx active center to greatly improve the current efficiency. Furthermore, we are also expected to explore the influence of electronic structure and types of active center on the current efficiency to describe the theoretical basis of high efficiency electrochemical synthesis of ammonia for further exploration of efficient electrochemical synthetic technology of ammonia.

发展零碳排放的氮阴极电还原合成氨技术，对缓解合成氨中化石能源的过度依赖，促进低碳经济发展，具有重要的现实意义。如何调制氮气还原电催化剂的活性中心以提高合成氨的电流效率则是发展该技术的关键。降低金属单原子碳基催化剂中氮配位金属（M-Nx）活性中心的N配位数能够促进氮气电还原从而提高电流效率。然而，构筑低配位M-Nx（X<4）结构并保持金属原子的单分散却面临严峻的挑战。基于此，本申请提出利用尿素构建的多边缘结构基底，通过“自上而下”的方式，捕捉无碳包覆的富金属大颗粒上热挥发迁移的金属原子，从而一步得到单分散低配位M-Nx结构；并引入模板，实现三维多孔低配位金属单原子碳基催化剂的控制合成，解决单分散低配位M-Nx结构难合成且暴露不充分的关键技术难题，以期提升电还原合成氨电流效率；分析活性中心种类及结构对电还原合成氨性能的影响规律，阐述高效电还原合成氨的理论依据，为高效氮阴极电还原合成氨奠定基础。

采用氮气和水直接电化学合成氨，因其低能耗无污染等特点，被认为有望取代哈伯固氮法成为下一代工业合成氨技术。尽管大量的电催化剂被开发用于催化氮气还原合成氨反应（NRR），但是NRR的电流效率仍然十分低下。因此，开发高电流效率的NRR催化剂成为了实现电化学合成氨的关键。本项目利用尿素构建的多边缘结构基底，通过“自上而下”的方式，捕捉无碳包覆的富金属大颗粒上热挥发迁移的金属原子，从而一步构筑了具有单分散低配位M-Nx结构的碳基单原子催化剂。基于此，本项目探索了单分散低配位M-Nx结构的碳基单原子催化剂的合成工艺，明晰了不同合成条件对于催化剂结构的影响规律，明晰了催化剂的结构衍生规律，建立了采用M-SCN配合物作为金属前驱体、尿素/葡萄糖作为氮/碳源的催化剂的合成方法学，有效地解决了单分散低配位M-Nx结构难合成且暴露不充分的关键技术难题。同时，验证了低配位M-Nx结构对电还原合成氨电流的促进作用，阐述了该类催化剂催化电还原合成氨的结构与性能间的构效关系，为合成高效电还原合成氨碳基单原子催化剂奠定基础。