Fe–N–C catalysts for oxygen electroreduction under external magnetic fields: Reduction of magnetic O2 to nonmagnetic H2O

Abstract

An extensive analysis of iron–nitrogen-carbon (Fe–N–C) electrocatalysts synthesis and activity is presented concerning synthesis conditions such as initial Fe content, pyrolysis temperature and atmosphere (inert N2, reducing NH3, oxidizing Cl2 and their sequential combinations) and the influence of an external magnetic field on their performance in oxygen reduction reaction (ORR). Thermosetting porous polymers doped with FeCl3 were utilized as the Fe–N–C catalysts precursors. The pyrolysis temperature was varied within a 700–900 °C range. The temperature and atmosphere of pyrolysis strongly affect the porosity and composition of the resultant Fe–N–C catalysts, while the initial amount of Fe precursor shows much weaker impact. Pyrolysis under NH3 yields materials similar to those pyrolyzed under an inert atmosphere (N2). In contrast, pyrolysis under Cl2 yields carbon of peculiar character with highly disordered structure and extensive microporosity. The application of a static external magnetic field strongly enhances the ORR process (herein studied in an alkaline environment) and the enhancement correlates with the Fe content in the Fe–N–C catalysts. The Fe–N–C materials containing ferromagnetic iron phase embedded in N-doped microporous carbon constitute attractive catalysts for magnetic field-aided anion exchange membrane fuel cell technology.