碳纳米碗负载六氮杂三萘撑基稠环微孔聚合物配位构筑单原子催化剂及机理研究

It remains a grand challenge to suppress the agglomeration of metal atoms and control the microstructure of active centers for non-noble metal single atomic catalysts for oxygen reduction reaction/oxygen evolution reaction (ORR/OER) occurring in the Zn-air battery. Based on hexaazatrinaphthylene polycyclic aromatic microporous polymers (C2N) possessing high content of coordination nitrogen atoms and the porous carbon nanobowls with the easily modified surface, the strategy of "regulating the chemical structure and orientation growth of C2N polymers to enhance the exposure of catalytic active sites of metal-nitrogen coordination species (M-Nx) with single metal atom" is proposed, on this base, the composite of carbon nanobowl@ C2N polymer is designed. Firstly, C2N nanosheets anchor and grow along the orientation perpendicular to the surface of carbon nanobowls, which have been modified with the aromatic amine group. Then, in order to increase the exposure degree of the aromatic nitrogen atoms in C2N polymers, the synthetic conditions are optimized to reduce the thickness of C2N nanosheets and develop the interstitial holes between nanosheets. To obtain highly dispersed M-Nx active sites through the coordination reaction of transition metal ions with aromatic nitrogen atoms, the type and volume of functional groups in the polymer skeleton are changed to regulate the chemical environment and spatial position of the aromatic nitrogen atoms. Finally, the roles of pore structure and the coordination structure, dispersion, and the content of M-Nx species in the catalytic performance of ORR/OER are elucidated through characterizing the microstructure and measuring the catalytic activities of the composite of carbon nanobowl@ C2N polymer, and then the catalytic mechanism is proposed after combining the results calculated by density functional theory. This study will provide theoretical and technical support for the development of new type ORR/OER dual functional catalytic materials.

锌-空电池用氧还原/析氧（ORR/OER）反应非贵金属基单原子催化剂，存在催化中心原子易团聚、微结构难控的问题。基于六氮杂三萘撑稠环微孔聚合物（C2N）可配位氮含量高和多孔碳纳米碗表面易改性的特点，本项目提出“调控C2N化学结构和取向生长以获得充分暴露的单原子分散金属-氮（M-Nx）催化活性位”的策略，构建碳纳米碗@C2N聚合物复合材料。拟利用先锚定、再生长的方法，在碳纳米碗表面获得取向生长的C2N纳米片；通过优化合成条件控制纳米片厚度并构筑间隙孔，促进芳香氮原子的充分暴露；进而调控聚合物骨架中基团类型和体积以改变芳香氮的化学环境和空间位置，利用金属离子与芳香氮配位，实现单原子分散M-Nx的构筑。通过微观结构和催化性能表征，阐明孔结构及M-Nx的配位结构、分散性和含量对催化性能的提升机制，结合密度泛函理论，提出催化机理。本研究为ORR/OER双功能催化新材料开发提供理论和技术支持。

空气极的氧还原/析氧（ORR/OER）反应效率决定着锌-空电池地充放电性能，开发廉价、高效ORR/OER双功能电催化剂是锌-空电池实用化的关键因素。通过本项目研究，构建了多种了ORR/OER双功能电催化剂： 1）基于纳米碗表面上原位生长铁、钴、镍等配位氮杂稠环微孔聚合物构建的含M-Nx催化剂活性位点的纳米碗表面@C2N基材料，其中CoO和单原子Co-Nx物种作为ORR/OER催化活性位点，可赋予锌-空电池1.498V的开路电压、716.5mAh g-1的放电比容量、75h的稳定放电，同时，还可以多次重复使用。这些性能优于商用Pt/C电催化剂。2）基于聚酰亚胺构建了内嵌Co9S8纳米粒子的N,S掺杂碳纳米管，该催化剂显示了低至0.76V的ORR和OER的电势差，优于大多数非贵金属双功能电催化剂。在锌-空气电池中，使充/放电电压差降低到0.65V，开路电位提高到1.539V、比容量增大到805mA hg、可稳定循环充放电48h，显著优于商用Pt/C和Ir/C混合催化剂。催化机理研究表明，石墨烯层中的N、S掺杂位点具有ORR催化活性，而Co9S8具有OER催化活性，二者协同作用是获得高催化活性的根本原因。3）聚酰胺和聚丙烯腈为前驱体构建了Fe3O4@N-C纳米花和Fe3O4/CoO@N-C纳米花，该类催化剂在锌-空电池中，可获得1.445V的开路电压、112 h的稳定放电、748.9 mA h g-1的电池比容量、136.8 mW cm-2的最大功率密度，性能显著高于 Pt/C和Ir/C混合商用催化剂。构效关系和理论计算研究表明，碳纳米花骨架N是ORR催化活性位点；Fe3O4是ORR和OER活性位点， Fe3O4中的氧空位显著促进了ORR和OER活性，引入的CoO作为OER活性位点，可提升催化剂的OER活性。此外，还开发了γ-FeOOH/ N，S共掺杂碳纳米片、Fe、N、S多元素共掺杂碳纳米碗、Rh/N掺杂碳纳米碗、N、F共掺杂的空心碳纳米球、低铂合金/碳纳米立方体等多种电催化剂，该类材料均具有优异的ORR催化活性。本研究为ORR/OER双功能催化新材料开发提供理论和技术支持。