Core-shell FeCo N-doped biocarbons as stable electrocatalysts for oxygen reduction reaction in fuel cells

A facile route is described for the synthesis of FeCo alloys encapsulated in the N-doped hierarchical carbon shells (denoted as Fe_xCo_100-x@N-doped C) by using a combined hydrothermal carbonization of cellulose and NH₃ microwave ammoxidation. Various spectroscopic measurements are used to characterize the physicochemical properties of Fe_xCo_100-x@N-doped C samples and their activity as well as stability in the oxygen reduction reaction (ORR) are investigated in alkaline electrolytes. The Fe_xCo_100-x@N-doped C samples exhibit the core FeCo bimetals alloying with N (verified by X-ray absorption spectroscopy [XAS] and transmission electron microscopy) and N-doped onto highly porous carbons in the shell (proofed by N₂ adsorption-desorption isotherms and X-ray photoelectron spectroscopy [XPS]). Among the Fe_xCo_100-x@N-doped C catalysts, the Fe₅₀Co₅₀@N-doped C with an atomic alloy ratio of FeCo (1:1) has a higher ORR performance (E_onset = −0.05 V vs Ag/AgCl) and a surpassing durability (via a 4-electron ORR route) in comparison to other Fe_xCo_100-x@N-doped C and commercial Pt/C catalysts. By XAS and XPS, the formation of Fe-N in the inner core and pyridinic-N on outer shell may be responsible for the superior ORR performance of Fe₅₀Co₅₀@N-doped C catalysts. These biomass-derived carbon composites with unique core-shell FeCoN@N-doped porous carbon structure prepared by using a time and energy saving microwave-assisted method could offer a possible cathodic electrode in fuel cell applications.