Fe/N/C hollow nanospheres by Fe(iii)-dopamine complexation-assisted one-pot doping as nonprecious-metal electrocatalysts for oxygen reduction

In this work, a series of hollow carbon nanospheres simultaneously doped with N and Fe-containing species are prepared by Fe³⁺-mediated polymerization of dopamine on SiO₂ nanospheres, carbonization and subsequent KOH etching of the SiO₂ template. The electrochemical properties of the hollow nanospheres as nonprecious-metal electrocatalysts for oxygen reduction reaction (ORR) are characterized. The results show that the hollow nanospheres with mesoporous N-doped carbon shells of ∼10 nm thickness and well-dispersed Fe₃O₄ nanoparticles prepared by annealing at 750 °C (Fe/N/C HNSs-750) exhibit remarkable ORR catalytic activity comparable to that of a commercial 20 wt% Pt/C catalyst, and high selectivity towards 4-electron reduction of O₂ to H₂O. Moreover, it displays better electrochemical durability and tolerance to methanol crossover effect in an alkaline medium than the Pt/C. The excellent catalytic performance of Fe/N/C HNSs-750 towards ORR can be ascribed to their high specific surface area, mesoporous morphology, homogeneous distribution of abundant active sites, high pyridinic nitrogen content, graphitic nitrogen and graphitic carbon, as well as the synergistic effect of nitrogen and iron species for catalyzing ORR.