多级碳纤维基过渡金属化合物氧还原/析出催化剂的设计合成、性能及机理研究

Li-O2 batteries have been the research focus of electrochemical energy systems because of their high energy density and power density in theory. Their typical cathodes are carbon materials modified by catalysts, such as Pt. However, the practical energy density, power density, and energy efficiency of Li-O2 batteries are relative low because of the easily blocked pores of carbon, the sluggish oxygen reduction/evolution reaction rate, and the high overpotential during charge process of Li-O2 batteries. Besides, the design principles for inexpensive carbon based transition metal compounds catalysts need further investigation. Regarding to the problems of the easily blocked pores of carbon, the sluggish oxygen reduction/evolution reaction rate, the high overpotential during charge, and the imperfect design principles for carbon based transition metal compounds catalysts, the present project will study the fabrication method and synthesis mechanism of nitrogen-doped brush-like carbon fiber flexible mats based transition metal oxide/nitride catalysts for oxygen reduction/evolution reactions. The mechanism about the effects of the microstructure of carbon fibers, the modification of transition metal oxide/nitride, and the interaction between the carbon matrix and transition metal oxide/nitride on the mass transfer characteristics and catalytic performance of the catalysts will be investigated in detail. The design theory of carbon based transition metal compounds composites as high performance catalysts for oxygen reduction/evolution reactions will be constructed. This study may be of high theoretical and practical value for the design, fabrication, and the application in Li-O2 batteries of superior performance and inexpensive oxygen reduction/evolution catalysts based on carbon- transition metal compounds. This project also will provide the theoretical direction on the research of carbon fiber based composites in other fields.

锂-氧电池因理论能量密度高、功率密度大成为电化学能源的研究重点，其正极材料常为修饰了催化剂（例如铂）的碳材料。但因碳基体易堵塞、氧还原/析出速率慢、氧析出过电压高而导致锂-氧电池的实际能量密度低、功率密度小、能量存储效率低等不足。此外，廉价的碳-过渡金属化合物催化剂的设计理论尚需完善。针对碳载体易堵塞、氧还原/析出速率慢、氧析出过电压高和复合催化剂设计原理不完善等问题，本课题拟研究氮掺杂毛刷状碳纤维柔性毡基过渡金属氧/氮化物氧还原/析出催化剂的制备方法和合成机理，探索碳纤维微观结构、过渡金属氧/氮化物修饰和其与碳载体相互作用对催化剂氧还原/析出催化性能的影响机理，建立高性能碳-过渡金属化合物基氧还原/析出催化剂设计理论。本项目的研究对高性能、低成本的碳-过渡金属化合物氧还原/析出催化剂的设计、制备和其锂-氧电池应用具有重要的理论意义和实用价值，也为碳纤维复合材料的其他研究提供理论指导。

针对氧还原/析出催化剂载体多孔碳易堵塞、传质性能差、传统催化剂昂贵、催化剂与载体间相互作用机制不明确等核心问题，本项目采用静电纺丝法和碳纳米管生长工艺，并结合碳材料表面修饰技术，制得了具有毛刷状结构的碳纳米管-碳纤维复合材料，发现了催化剂对碳纳米管和复合纤维微观结构的影响机制，得到了高性能氧还原/析出催化剂。在此基础上，我们开展了三明治状Fe-N-石墨烯复合材料的氧还原性能研究，其极限电流密度高达6 mA/cm2；利用锌基MOF材料实现了Co-N-C催化剂性能调控，将该四电子反应催化剂的极限电流密度提高到6.2 mA/cm2；建立了基于SiO2造孔和氮掺杂介孔石墨烯催化剂的合成方法；发现了氧化钨的氧空位对其析氢性能的影响机制；制备了WO3/C共包覆CoO催化剂。另外，在碳纤维催化剂载体的氧还原/析出研究的基础上，我们建立了一种基于相分离原理制备金属氧化物@碳核壳纤维的方法，填补了无模版合成核壳纤维的空白，且以此方法得到了中空多孔碳纤维，研究发现了其具有500 mA h/g的可逆储钠性能。在碳纤维复合纤维结构设计方面，我们设计并制备了具有电线管结构的TiO2-Sn@C纳米纤维，得到了400次循环后容量仍高达413 mA h/g的钠离子电池负极。本项目的研究促进了碳纤维与碳纳米管这两类碳材料在交叉学科的研究，对构建新型碳纤维复合材料具有指导意义，对扩展碳材料在电池相关领域的研究提供思路，为可控、可设计碳材料在能源、催化等领域的大规模应用奠定了基础。