热解微量Fe掺杂ZIF-8/PAN静电纺丝纤维制备1D多孔Fe-N-C基ORR电催化剂

Preparation of 1D Porous Fe-N-C based ORR Electrocatalysts by Pyrolysis of Trace Fe-doped ZIF-8/PAN Electrospun Fibres

开发简单、高效地批量制备多孔Fe-N-C催化剂的方法对于其大规模应用具有重要意义。静电纺丝法是一种可以很简单地通过增加针头数量来大规模生产碳基催化剂的常用方法, 而如何通过调控成分来控制静电纺丝纤维热解产物的孔结构和成分还存在很多困难。本文通过热解微量Fe掺杂ZIF-8颗粒与PAN的静电纺丝纤维制备了具有大量开放孔的高度石墨化的一维Fe-N-C催化剂。利用扫描电子显微镜、透射电子显微镜、X射线衍射、拉曼光谱、X射线光电子能谱和氮气吸附-脱附测试对材料进行了结构和成分分析。通过循环伏安法、线性扫描伏安法、旋转环盘电极测试表征了催化剂的电催化ORR性能。结果表明, 微量Fe掺杂实现了封闭孔向开放孔的转变, 将孔内活性位点暴露出来使其能够高效地参与反应。热解过程中Fe能够催化表面石墨结构的形成, 减小了电荷转移阻力, 间接提高了ORR反应速率。高活性Fe-N-C和石墨-N位点的引入, 孔结构的优化和石墨化程度的提高, 使5%Fe-NC获得了超越商业20%Pt/C的优异ORR催化性能。

The development of a simple and efficient method for batch preparation of porous Fe-N-C catalysts is of great significance for it large-scale application. Electrostatic spinning is a common method that can be used to produce carbon-based catalysts on a large scale simply by increasing the number of needles. However, it is still difficult to control the pore structure and composition of the pyrolysis products of electrostatically spun fibers by modulating the composition. In this paper, highly graphitized one-dimensional Fe-N-C catalysts with a large number of open pores were prepared by pyrolysis of electrospun fibres of trace Fe-doped ZIF-8 particles with PAN. The materials were structurally and compositionally analyzed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption test. The electrocatalytic ORR performance of the catalysts was characterized by cyclic voltammetry, linear scanning voltammetry, and rotating ring-disk electrode tests. The results show that trace Fe doping achieves a transition from closed to open pores, exposing the active sites within the pores to allow them to participate efficiently in the reaction. Fe could catalyze the formation of surface graphite structures during pyrolysis, which reduces the charge transfer resistance and indirectly increases the ORR reaction rate. The formation of highly reactive Fe-N-C and graphite-N sites, the optimization of pore structure and the enhancement of graphitization allow 5% Fe-NC to achieve excellent ORR catalytic performance beyond that of commercial 20% Pt/C.