Fe/Fe3C Nanoparticles Encapsulated in N-Doped Hollow Carbon Spheres as Efficient Electrocatalysts for the Oxygen Reduction Reaction over a Wide pH Range

Nonprecious-metal-based electrocatalysts with low cost, high activity, and stability are considered as one of the most promising alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR). Herein, an economical and easy-to-fabricate catalyst is developed, that is, Fe/Fe3C embedded in N-doped hollow carbon spheres (Fe/Fe3C/NHCS), which gave the half-wave potential of 0.84V in 0.1m KOH, similar to the commercial Pt/C catalyst. Surprisingly, the favorable ORR performance of the as-prepared catalyst was obtained in both acidic and neutral conditions with almost a four-electron pathway and low H2O2 yield, which desirable the development of the proton exchange membrane (PEM) and microbial electrolysis cell (MEC) technology. Additionally, the obtained catalyst demonstrated better long-term stability and high methanol tolerance over a wide range of pH. These features could be mainly attributed to the synergistic effect between Fe/Fe3C and Fe-N-x sites, the hollow structure with mesopores, and the well-dispersed Fe/Fe3C nanoparticles owing to the existence of the abundant hydrophilic groups within the HCS precursor. As such, designing an efficient and cheap ORR catalyst that can operate at alkaline, acidic, and neutral solutions is highly desirable, yet challenging.