In-situ Preparation Of Fe/N/C Catalysts And Their Performance For Electrocatalytic Oxygen Reduction

Design and synthesis of inexpensive non-precious metal catalysts for oxygen reduction reaction (ORR) with high performance is one of most efficient paths to reduce the cost and accelerate the process of commercialization of fuel cell. TM/N/C composites have been considered as one of the most potential substitute for noble metal catalysts. However, the biggest obstacle for developing high-performance TM/N/C is the multi-step and complex synthetic process, which not only weakens the advantage of TM/N/C on production costs, but also leads more difficulty for the controllable construction of the nanostructure, especially the interfaces among different constituents, one of most important factors for the electrocatalytic activity and stability of the catalysts. Based on the above analysis, this thesis presents an in-situ method to construct high-performance Fe/N/C catalysts with well-defined core-shell nanostructure from cheap raw materials. And enhanced interface interaction was then achived by optimizing the synthesis conditions, resulting in an improved electrocatalytic cativity and stability. Further, the effect of catalyst’structure and composition on the electrocatalytic performance has been investigated systematically, providing the basis for deep reveal of real active sites and catalytic mechanism for ORR.(1) Fe/g-C3N4was employed as the single precursor for facile synthesis of one-dimensional core-shell Fe@NCNT catalyst by in situ method. The Fe nanoparticles confined in NCNT and the N-doped active sites on NCNT can synergistically catalyze the ORR. As a result, the prepared Fe@NCNT-900possessed a good activity and current efficiency with a high catalytic current density of5.19mA/cm2and electron transfer number of3.90, respectively. Second heat treat of prepared samples at900℃can further enhance the catalytic activity. Optimized catalyst has a good stability with a current retention rate of85.7%after i-t test of10000s.(2) The g-C3N4was employed as two-dimensional (2D) self-sacrificing template for one-step synthesis of lotus seedpod-liked Fe/Fe3C@GC@NG catalysts with well-defined hierarchical core/shell structure. In situ formed g-C3N4was used as template and nitrogen precursor and glucose and FeSO4-7H2O as carbon and Fe precursor, respectively. The generated Fe/Fe3C@GC nanocapsules were embedded into the interlayer of graphene to form sandwich-liked structure, which can efficiently protect graphene from stacking and facilitate the fast transport of charge and materials. Meanwhile hierarchical core/shell structure by in situ synchronous construction can achieve a strong interface interaction, which benefits for the improvement of electrocatalytic activity and stability of prepared catalysts. Electrochemical tests show that the prepared Fe/Fe3C@GC@NG-20catalyst can reach a high catalytic current density of5.32mA/cm2and electron transfer number of3.80; the stability was enhanced with a current retention rate of91%after i-t test of6000s.(3) Iron phthalocyanine (FePc) was employed as the single precursor for one-step synthesis of strong coupled and hierarchical core-shell structured catalysts (Fe/N/G) assisting with2D self-sacrificing template. Combining the ideas of single precursor and2D self-sacrificing template, the interface interaction between different microstructures of prepared catalysts was enhanced significantly, promoting the further improvement of electrocatalytic activity and stability of prepared catalysts. As a result, the prepared Fe/N/G (60)-900catalyst possesses a high-performance catalytic property with a high catalytic current density of5.80mA/cm2and electron transfer number of3.90. The important is that the stability was improved significantly with a high current retention rate of97.5%after i-t test of8000s.