异原子过渡金属和磷共掺杂碳的制备及其对氧气还原催化机理的研究

The development of low cost and highly active non-noble metal catalysts will lead to a significant cost reduction brought by Pt in the Proton Exchange Membrane Fuel Cells(PEMFCs).Heteroatoms of transition metal and phosphorus co-doped carbon catalysts for the oxygen reduction reaction at the cathode of the PEMFC are proposed in this project. The co-doping of transition metal and phosphorus in carbon will be used to modify the electronic structure of the carbon and the catalytic activiy of the carbon for the oxygen reduction reaction.The effect of doping with the electron-donor heteroatoms on the active sites of the catalysts and the oxygen reduction reaction mechanism will be studied.The debates on the active sites of electron-donor heteroatom-doped carbon and the oxygen reduction mechanism will be addressed. The transition metal and phosphorus co-doped carbon catalysts will be prepared by a template method with phosphorus-containing ionic liquids,carbon-containing organic compounds and transition metal salts as precursors.The nature of the active sites will be studied by in-situ X-ray Diffraction and in-situ X-ray Absorption Spectroscopy. The intermediates produced in the oxygen reduction reaction will be studied by in-situ Raman. Electrode kinetics of the oxgyen reduction reaction on the prepared catalysts will be investigated. The mechanism of the oxygen reduction reaction on the carbon doped with electron-donor heteoatoms will be elucidated based on the above studies. These studies will lay a solid theoretical and experimental foundation for designing and preparing highly active heteroatom-doped carbon non-noble catalysts for the oxygen reduction reaction.

寻求低成本和高催化活性的非贵金属催化剂，是解决质子交换膜燃料电池(PEMFC)由Pt基贵金属催化剂带来的成本高问题的重要途径。本项目提出制备异原子过渡金属和磷共掺杂碳作为阴极氧气还原的催化剂。通过过渡金属和磷共掺杂调控碳的电子结构以及对氧气还原的催化活性，针对异原子掺杂碳催化剂的催化活性位以及对氧气还原机理存在的争议，研究具有给电子性异原子掺杂对催化活性位的形成以及对氧气还原机理的影响。以含磷的离子液体、含碳有机物和过渡金属盐为前驱体，采用模板法制备材料。以原位X-射线衍射（XRD）和原位X-射线吸收谱（XAS）研究催化剂的催化活性位；利用原位拉曼光谱分析氧气还原的中间产物，结合氧气电极过程动力学研究，阐明具有给电子性异原子掺杂碳对氧气还原的催化机理，为设计、制备高催化活性的异原子掺杂碳非贵金属催化剂提供理论和实验基础。

针对质子交换膜燃料电池Pt基贵金属催化剂带来的催化活性稳定性差和成本高等问题，以异原子掺杂碳作为阴极氧气还原催化剂，通过过渡金属元素钴 (Co)、铁(Fe)、镍(Ni)、锰（Mn）和磷（P）共掺杂、其它非金属元素氮(N)，硫(S)，硼（B）和P共掺杂调控碳的电子结构及对氧气还原反应（ORR）的催化活性。考察了微观结构、形貌、与其它原子共掺杂、异原子的键合环境等对P掺杂碳的催化性能的影响，进一步发展了制备异原子掺杂碳的新方法，探讨了P掺杂碳的催化活性位和对氧气还原的催化机理。在P和Co, Fe，Ni, Mn共掺杂碳体系中，制备了P和Co共掺杂高比表面积微孔碳，P和Co共掺杂介孔碳，P和Co共掺杂石墨烯，P和Fe共掺杂微孔碳，P和Ni共掺杂微孔碳，P和Mn共掺杂微孔碳，研究结果表明过渡金属的引入可以进一步提高碳材料对氧气还原的催化性能；不同过渡金属共掺杂，其催化活性不同。我们初步提出了过渡金属（Transition metal,TM）和P共掺杂碳的可能的催化活性中心位为TM-Px（x是与过渡金属原子配位的P原子数）。在此基础上，制备了其它异原子（N，S，B）和P共掺杂碳，其中包括P、N二元共掺杂石墨烯，P、N和S三元共掺杂分级多孔碳和具有核壳结构的N、P、B三元共掺杂生化碳材料，研究结果表明，多元共掺杂可以显著提高碳的氧气还原催化活性，其高的催化活性主要来自于多元异原子掺杂的协同作用。考虑到三相界面对物质传输的重要性，制备了具有特殊形貌的P掺杂空心碳球和N掺杂空心立方体碳，探索了空心碳对气、液、固三相物质传输以及最终氧气还原催化性能的影响。研究结果表明所制备P掺杂碳材料对氧气还原的较高催化活性不仅来自于P掺杂引起碳的电荷不对称性对O2的吸附和还原的促进，而且来自于催化剂特殊的结构对氧气还原过程中物质传输的改善。项目实验结果为设计燃料电池的高效阴极催化剂提供了新思路。