Synergistic melamine intercalation and Zn(NO₃)₂ activation of N-doped porous carbon supported Fe/Fe₃O₄ for efficient electrocatalytic oxygen reduction

Developing inexpensive, efficient and good stability transition metal-based oxygen reduction reaction (ORR) electrocatalysts is a research topic of great concern in the commercial application of fuel cells. Herein, with zinc nitrate as activator, iron nitrate as active component and melamine as intercalating agent and nitrogen source, an N-doped porous carbon supported Fe/Fe₃O₄ (Fe/Fe₃O₄@NC) catalyst is successfully synthesized by an impregnation-calcination method combined with freeze-drying technique. The positive onset potential (E _onset), half-wave potential (E _1/2) and limiting current density (J _L) of the optimal Fe/Fe₃O₄@NC catalyst are 1.012, 0.90 V vs. RHE and 5.87 mA cm^-2, respectively. Furthermore, Fe/Fe₃O₄@NC catalyzes ORR mainly through a 4e^- pathway, and the yield of H₂O₂ is less than 5%. It also manifests a robust stability after 5000 CV cycles of ADT testing, and the half-wave potential is only negatively shifted 17 mV. The structural characterization and experimental results further suggest that the outstanding ORR electrocatalytic performance of the Fe/Fe₃O₄@NC catalyst benefits from the synergetic effect of zinc nitrate activation and nitrogen doping, which can greatly improve the specific surface area, thus better dispersing more metal active sites. This work puts forward a simple and practicable way for preparing high-performance non-noble metal-based biomass ORR electrocatalysts.