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

Abstract

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.