Fe-N-C单原子催化剂在燃料电池中具有广阔的应用前景，研究活性位Fe-Nx的电子结构对其本征催化活性的影响规律对于理解氧还原反应（ORR）机制和Fe-N-C催化剂的优化具有重要价值。自旋态是描述中心Fe电子结构的重要参数之一，但有关Fe的自旋态与其催化活性之间定量关系的研究仍鲜有报道；另外，目前在合成策略上也缺乏调控Fe自旋态的有效方法。基于以上背景，本论文借助电化学表征、电子顺磁共振波谱（EPR）和电子能量损失谱（EELS）等方法，研究了单原子Fe催化剂中Fe的自旋态与其催化活性值之间的定量关系。论文首先研究了金属有机框架化合物（ZIF-8）衍生的Fe-N-C单原子催化剂的自旋态与催化性能，对比了共掺杂法和浸渍吸附法这两种目前主流的合成方法。对于共掺法合成的Fe-ZIF-8前驱体，提高热解温度可明显改善单原子Fe的本征催化活性。而由浸渍法合成的Fe-N-C催化剂，其本征活性对热处理温度不敏感。EPR和EELS分析均表明，共掺法催化剂的合成温度、自旋态与催化活性之间存在很强的相关性：热解温度越高，Fe中心原子的自旋态越低，催化活性越高。这一方面是由于高的热解温度促进了石墨氮含量的相对提高，而石墨氮的增加可降低Fe中心的自旋态；另一方面可能是由于高温热解促进了Fe的配位构型从四面体型向平面四方型的转变，使Fe-N之间的相互作用增强，有利于低自旋态Fe中心的形成。进一步研究了前驱体中Fe的价态对Fe-N-C中Fe自旋态和催化活性的调制作用。发现Fe2+前驱体能够提高共掺法单原子Fe的本征催化活性，这应该与Fe2+更有利于形成低价态和低自旋态的Fe-N4有关。但这种作用随热解温度的升高而减弱，因为在高温下热解温度是更主要的影响因素。Fe2+对于提高浸渍吸附法制的备Fe-N-C催化剂催化活性的作用不明显。采用优化的Fe-N-C催化剂作燃料电池阴极催化层，在H2-O2条件下的峰值功率密度可达800 mW cm-2。最后，研究了共掺法中前驱体溶剂的影响。相对于纯甲醇溶剂反应体系，水的加入能够改变2-甲基咪唑去质子化的能力，影响了ZIF-8晶体的动力学生长过程及其形貌；同时，水能够提高Fe离子在ZIF-8晶体中的掺杂效率，从而进一步改善Fe-N-C催化剂的ORR催化性能。

Single-atom catalysts Fe-N-C have broad application prospects in fuel cells. The influence of the electronic structure of Fe-Nx on its intrinsic catalytic activity has important theoretical value for the in-depth understanding of the oxygen reduction reaction mechanism and the further optimization of the Fe-N-C catalyst structure. The spin state is one of the important parameters describing the electronic structure of the central Fe, there are still few reports on the quantitative relationship between the spin state of the central Fe and its intrinsic catalytic activity. In addition, there is currently a lack of effective methods to control the Fe spin state in synthesis. Based on the background, this thesis uses electrochemical characterization, electron paramagnetic resonance spectroscopy (EPR) and electron energy loss spectroscopy (EELS) to focus on the quantitative relationship between the spin state of Fe and its intrinsic catalytic activity in Fe-N-C single-atom catalysts.The thesis first studied the spin state and catalytic performance of Fe-N-C single-atom catalysts derived from metal organic framework compounds (ZIF-8), and compared the two current mainstream synthesis methods, co-doping method and immersion adsorption method. For the Fe-ZIF-8 precursor synthesized by the co-doping method, increasing the pyrolysis temperature can significantly improve the intrinsic catalytic activity of the catalyst. The intrinsic activity of Fe-N-C catalyst synthesized by impregnation method is not sensitive to heat treatment temperature. Both EPR and EELS analysis show that there is a strong correlation between the synthesis temperature, spin state and catalytic activity of the co-doped catalyst: the higher the pyrolysis temperature, the lower the spin state of the Fe central atom, and the higher the catalytic activity. On the one hand, the high pyrolysis temperature promotes the relative increase of the graphite nitrogen content, and the increase of graphite nitrogen can reduce the spin state of the Fe center. On the other hand, it may be due to the high temperature pyrolysis that promotes the coordination configuration of Fe. The transition from a tetrahedral type to a flat tetragonal type enhances the interaction between Fe-N, which is conducive to the formation of low-spin Fe centers.The modulation effect of the valence state of Fe in the precursor on the spin state and catalytic activity of Fe in Fe-N-C was further studied. It is found that the Fe2+ precursor can improve the intrinsic catalytic activity of Fe-N-C catalyst. EELS results show that the single atom Fe of the catalyst obtained by using the Fe2+ precursor has a lower spin state. However, Fe2+ does not significantly improve the catalytic activity of Fe-N-C catalysts prepared by the impregnation method, which may be due to differences in the active site structures obtained by different preparation methods. Finally, the influence of the precursor solvent in the co-doping method is studied. Compared with the pure methanol solvent reaction system, the addition of water can change the ability of 2-methylimidazole to deprotonate and affect the kinetic growth process and morphology of the ZIF-8 crystal. At the same time, water can increase the doping efficiency of Fe ions in the ZIF-8 crystal, thereby further improving the ORR catalytic performance of the Fe-N-C catalyst. This paper verifies the relationship between the ORR catalytic activity of Fe-N-C catalyst and the central Fe spin at the experimental level, and provides a new perspective for the study of active sites and performance improvement of the catalyst.