ZIF-67-Derived Dodecahedral Co@N-Doped Graphitized Carbon Protected by a Porous FeS₂Thin-Layer as an Efficient Catalyst to Promote the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) plays an irreplaceable role in many energy-conversion processes. Low-cost catalysts with high activity and stability are eagerly needed to improve the sluggish ORR kinetics. Herein, we use a simple hydrothermal method to evenly deposit iron disulfide (FeS 2, as shell) on the surface of dodecahedral Co@N-doped graphitized carbon (Co@DNC, as core) with ZIF-67 dodecahedrons as the precursor. Co@DNC@FeS 2 -0.5 (Co@DNC-to-FeCl 3 ·6H 2 O mass ratio of 0.5) catalyst shows a comparable ORR catalytic activity (onset potential of 0.942 V and half-wave potential of 0.846 V, vs reversible hydrogen electrode) to commercial Pt/C (20 wt %) in alkaline media. The charge transfer resistance (4.06 Ω) of Co@DNC@FeS 2 -0.5 is smaller than that of Pt/C (6.72 Ω), indicating that Co@DNC@FeS 2 -0.5 facilitates a fast Faradaic process and charge transfer kinetics for the ORR. The core@shell structure and highly active moieties of Co@DNC@FeS 2 -0.5 contribute to the high ORR activity. DNC-wrapped Co/CoO (originated from the oxidation of surface Co 0 ) possesses the positive charges to prioritize the adsorption of O 2 on the Co–N x (Co atom binds to pyridinic N) active sites, and then, the S–S bonds in FeS 2 with multivalent redox activity can supply/transfer the electrons to Co–N x to boost the ORR via a 4e – pathway. Moreover, the DNC@FeS 2 shell with a porous structure can protect the active sites on the Co cores and accelerate the mass transfer of ORR-related species (O 2, OH –, etc.) to the active sites. This study provides a novel strategy to enhance ORR activity using the core@shell structured catalysts originating from zeolite imidazole frameworks.