ZIF-67-Derived Dodecahedral Co@N-Doped Graphitized Carbon Protected by a Porous FeS<sub>2</sub>Thin-Layer as an Efficient Catalyst to Promote the Oxygen Reduction Reaction
Mingyang Liu, Min Zhang, Peng Zhang, Zipeng Xing, Baojiang Jiang, Yu Yang, Zhuang Cai, Jiahuan Li, Jinlong Zou
Abstract
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 (FeS2, as shell) on the surface of dodecahedral Co@N-doped graphitized carbon (Co@DNC, as core) with ZIF-67 dodecahedrons as the precursor. Co@[email protected] (Co@DNC-to-FeCl3·6H2O 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@[email protected] is smaller than that of Pt/C (6.72 Ω), indicating that Co@[email protected] facilitates a fast Faradaic process and charge transfer kinetics for the ORR. The core@shell structure and highly active moieties of Co@[email protected] contribute to the high ORR activity. DNC-wrapped Co/CoO (originated from the oxidation of surface Co0) possesses the positive charges to prioritize the adsorption of O2 on the Co–Nx (Co atom binds to pyridinic N) active sites, and then, the S–S bonds in FeS2 with multivalent redox activity can supply/transfer the electrons to Co–Nx to boost the ORR via a 4e– pathway. Moreover, the DNC@FeS2 shell with a porous structure can protect the active sites on the Co cores and accelerate the mass transfer of ORR-related species (O2, 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.