Hollow carbon spheres codoped with nitrogen and iron as effective electrocatalysts for oxygen reduction reaction

Design and engineering of low-cost, effective catalysts for oxygen reduction reaction (ORR) plays a critical role in the development of fuel cells and metal-air batteries. Herein, we describe a facile template-assisted strategy for the fabrication of hollow porous carbon spheres codoped with nitrogen and iron species (FeNC) for ORR electrocatalysis. The samples are synthesized via one-step pyrolysis of a core-shell precursor, which is prepared by in-situ growth of a Fe-doped zeolite imidazolate framework (ZIF) shell onto the surface of polystyrene nanoparticles. The obtained FeNC composites exhibit a unique hollow structure with a large surface area, hierarchical porosity, and abundant FeNx sites. Notably, the sample prepared at 950 °C (FeNC-950) exhibits the best ORR activity among the series in alkaline media (with an onset and half-wave potential at +0.94 and + 0.84 V vs. RHE, respectively), a performance on par with that of Pt/C and leading relevant catalysts reported in recent literature, where ORR proceeds mostly via the efficient four-electron reduction pathway. The FeNC-950 catalyst also displays superior stability and tolerance to methanol, as compared to commercial Pt/C. The results suggest that high-performance ORR catalysts can be derived by deliberate structural engineering of the metal-organic framework precursors.