过渡金属-氮掺杂碳氧还原催化剂高密度活性位点的形成机制和结构演化规律

It is extremely desirable to develop transition metal-nitrogen doped carbon (M-Nx/C) material as the highly active catalyst for oxygen reduction reaction at the cathode of fuel cell. However, there are still some challenges in its practical application, including low density of active sites and poor durability. In this proposal, we plan to develop porous nanofiber M-Nx/C catalysts by electrospinning and plasma pyrolysis at low temperature, aiming to achieve controllable morphology, high density of active sites, well dispersion of component and good long-term stability. Owing to the nano-space confinement within nanofibers and the lower temperature by plasma pyrolysis, the N losing and the metal cluster agglomeration during thermal treatment will be prohibited efficiently, which will help to format the M-Nx/C sites with high density. The formation mechanism of M-Nx/C sites with high density will be discussed. Furthermore, the physical stability of the nanofibers and the distribution uniformity of the active sites will be improved by controlling the nanofiber structure, including the size, morphology, specific surface area and porosity, etc. The effects of the types, density of metal-Nx, and carbon graphitization on the electro-catalytic activity and the durability of such catalysts for ORR will be demonstrated. The structural evolvement of metal-Nx sites at different pH will be revealed up. We expect to provide a new method to synthesize metal-Nx catalysts with favorable high density of active sites and long-term stability, and to approach the development of non precious catalysts with basic theory and technical supporting.

面向质子交换膜燃料电池应用的过渡金属-氮掺杂碳(M-Nx/C)氧还原电催化剂存在活性位点密度低、催化剂耐久性差等问题，本项目提出通过静电纺结合等离子体低温热解等方法研制结构可控、催化活性位点密度高、活性组分分布均匀、耐久性好的纳米纤维状M-Nx/C催化剂。通过纳米纤维的空间限域效应和等离子体低温热解等，降低M-Nx/C形成过程中N元素流失和过渡金属物种聚集，实现M-Nx/C活性位点密度的最大化，阐明高密度活性位点的形成机制；通过催化剂尺寸、形貌、比表面、孔隙率等调控，提高催化剂的结构稳定性和活性组分分布的均匀性，探讨M-Nx/C活性位点结构、碳的石墨化程度等与催化活性和耐久性之间的关系，揭示不同酸碱度下M-Nx/C活性位点的结构演化规律，发展高效电催化剂的制备方法，研制具有高密度催化位点、高耐久性等的纳米纤维M-Nx/C催化剂，为非贵金属催化剂的发展及应用提供科学理论和技术基础。

面向质子交换膜燃料电池应用的过渡金属-氮掺杂碳(M-Nx/C)氧还原电催化剂存在活性位 点密度低、催化剂耐久性差等问题，本项目基于纳米限域原理，通过静电纺丝、高温热处理和二次氨气热处理等方法，可控制备了一系列过渡金属(Fe、Co)、N共掺杂及包覆FexN或Co纳米粒子核壳结构的碳纳米纤维氧还原催化剂，调控了纳米纤维的组成和多孔结构，阐明了催化活性位点的结构、形成机制和稳定机制。通过源头设计，构筑了三维分级多孔的单分散Fe-N-C催化剂、三维网络石墨烯纳米带/碳纳米管Fe-N/C催化剂、铁掺杂沸石咪唑骨架材料（Fe-ZIF）诱导合成Fe-N-C分级多孔催化剂、源头设计Co/Zn双金属掺杂含氮碳基催化剂等，显著提升了活性位点密度，实现在锌空气电池和氢氧燃料电池上的应用。