强非共价键作用增强的电荷转移及其与纳米碳材料ORR催化活性的关系

Because the nitrogen-doped nano-carbon material is not an appropriate module to study the relationship between the charge transfer effect and the electrochemical catalytic activity of the nano-carbon material for the oxygen reduction reaction (ORR), in this project the molecular doping method will be used to control the type and the content of the electron donor and electron acceptor in nano-carbon materials, and the strong noncovalent self-assembly approach will be used to enhance the charge transfer between the organic electron donor/acceptor and nano-carbon materials, aiming at the research on the relationship between the charge transfer effect and the catalytic activity of the nano-carbon material in the ORR reactions. In this application, employing pyrene based nitrogenous large-conjugated molecules/nano-carbon assemblies, and the electron donor/acceptor based on graphene quantum dot/linkers with dipyrene-terminal group/nano-carbon assemblies as the modules, the relationship between the charge transfer effect and the electrochemical catalytic activity of the nano-carbon material will be investigated by the enhanced charge transfer due to the strong π-π interactions and the varied extent and direction of the charge transfer from controlling the type and the content of the electron donor or electron acceptor as well as the linkage between electron donor/acceptor and the nano-carbon material. Finally, the best type and degree of the charge transfer for enhancing the electrochemical catalytic activity in ORR reactions will be found, and the catalytic mechanism of nano-carbon in ORR reactions and the controlling factors will be properly analyzed, which can lay the theoretical foundation for designing highly effective metal-free nano-carbon catalysts.

由于氮原子掺杂纳米碳材料不适合作为研究电荷转移效应与其ORR催化活性关系的实验模型，本申请拟以分子掺杂的方法控制纳米碳材料中电子给受体的类型和含量，通过强非共价键自组装方式增强有机电子给受体和纳米碳材料的分子间电荷转移，达到研究电荷转移与纳米碳材料ORR催化活性关系的目的。本申请以芘基含氮大共轭分子/纳米碳自组装体、石墨烯量子点电子给受体/双芘端基连接体/纳米碳自组装体为模型，通过强π-π作用增强电子给受体与纳米碳材料之间的电荷转移，通过改变电子给受体种类、数量、双芘端基连接体等控制电荷转移的大小和方向，研究电荷转移效应和纳米碳材料ORR催化活性之间的关系。最终明确非金属纳米碳材料中何种形式、何种程度的电荷转移最有利于催化ORR反应，分析纳米碳材料催化ORR的机制和控制步骤，为设计高效的非金属纳米碳材料催化剂奠定理论基础。

本项目针对非金属纳米碳材料催化ORR机理不清、选择性难控制和活性差的难点，重点开展以下两方面研究：一是大环共轭有机分子/纳米碳催化ORR的机制和选择性；二是基于得到的催化机制构筑高活性纳米碳ORR催化材料。研究以“大环共轭有机分子/纳米碳材料的电荷转移与催化ORR选择性和活性关系”和“氮掺杂纳米碳材料催化ORR活性位点的本质”为主线，取得了一系列研究成果。项目构筑了不同个数硝基修饰的大环共轭苝酰亚胺/碳纳米管、不同取代基修饰的卟啉/碳纳米管、吡嗪并喹喔啉为基础的二维全共轭有机骨架/碳纳米管、高吡啶氮含量的纳米碳等ORR催化体系。通过这些体系的研究明确了：1、大环共轭分子/纳米碳自组装体分别从电极接受一个电子或两个电子，形成负离子自由基或双自由基。以负离子自由基为活性中间体主要发生2e ORR，以双自由基为中间体发生4e ORR；负离子自由基和双自由基同时存在则2e ORR、4e ORR同时发生；2、大环共轭分子/纳米碳的ORR催化选择性通过负离子自由基或双自由基的生成电位控制；3、负离子自由基和双自由基的形成电位能通过组装体内共轭分子和纳米碳材料之间的电荷转移改变，从而控制催化ORR的选择性；4、伴随纳米碳材料的平面内吡啶氮掺杂，必会形成面内孔缺陷，该缺陷上含有两个未成对的单电子，类似于共轭分子/纳米碳材料的双自由基，能高效催化4e ORR，这是对吡啶氮掺杂纳米碳材料高效催化4e ORR 机理的发展和新理解。同时，项目拓展了申请书中所提出的研究思路和研究内容，开展了多种基于纳米碳材料应用于OER、HER、二次电池等能源化方面研究。研究项目在化学、材料期刊上发表SCI论文27篇，包括1篇ACS Appl. Mater. Interfaces，1篇ACS Appl. Energy Mater., 1篇Chem. Eng. J., 6篇Electrochim. Acta等。