Fe-N_<i>x</i> Sites Enriched Carbon Micropolyhedrons Derived from Fe-Doped Zeolitic Imidazolate Frameworks with Reinforced Fe-N Coordination for Efficient Oxygen Reduction Reaction

Abstract

Rational design and facile synthesis of highly active and stable electrocatalysts for oxygen reduction reaction (ORR) are crucial in the field of metal-air batteries. Here, we present a facile two-stage thermal synthesis of Fe-N codoped porous carbon (Fe-N/C) with abundant Fe-Nx active sites and mesopores from Fe-doped ZIF-8 precursors. The first-stage preheating treatment of the Fe-doped ZIF-8 precursors before the second-stage carbonization is the key to boost the coordination between the doped Fe and N-containing ligands, which contributes to a higher N content and more Fe-Nx sites in the final carbonized product. Besides, the preheating and Fe-doping both affect the morphology, porous structure, and catalytic performance of the fabricated Fe-N/C. The optimized Fe-N/C catalyst exhibits an outstanding ORR catalytic performance with a half-wave potential of 0.88 V and limiting current density of 6.0 mA cm–2 in 0.1 M KOH. A Mg-air battery assembled with a neutral electrolyte using the optimized Fe-N/C catalyst as the cathode exhibits an excellent power density of 72 mW cm–2 at 0.72 V. This developed two-stage synthesis strategy is facile, and the preheating stage could be integrated into any carbonization process as an intermediate step for the fabrication of various metal, N codoped carbon materials with enhanced electrocatalytic performance.