Iron/Nitrogen co-doped mesoporous carbon synthesized by an endo-templating approach as an efficient electrocatalyst for the oxygen reduction reaction

Iron/Nitrogen-doped carbon catalysts are considered to be one of the most promising candidates to replace platinum-based catalysts for the oxygen reduction reaction in the cathode of the fuel cell. Herein, we demonstrate a simple and cost-effective strategy for the fabrication of Fe-N-C-mesoporous-carbons involving the carbonization of calcium citrate followed by a post-treatment with urea and ammonium sulfate iron (II). The synthesized materials exhibit high values of surface area, large nitrogen and iron contents. The iron is present in two configurations: i) gamma-iron phase and ii) iron coordinated to nitrogen (Fe-N-x). When used as an electrocatalyst in basic electrolyte, the Fe-N-C material predominantly catalyzes the four-electron pathway with an onset potential of 0.91 V and a half-wave potential of 0.81 V. In acidic electrolyte, the optimized catalyst exhibits an onset potential of 0.73 V. The experimental results show that the N-functionalities and the Fe-N coordination sites play a major role in catalytic performance in both kinds of electrolytes and that the gamma-iron phase has little or no catalytic effect. In this regard, pure N-doped carbon shows to be better catalyst than pure Fe-doped carbon. Hence, these results provide useful guidelines for the development of highly active and cost-effective ORR catalysts.