Zeolitic Imidazolate Framework‐Derived Core‐Shell‐Structured CoS2/CoS2‐N‐C Supported on Electrochemically Exfoliated Graphene Foil for Efficient Oxygen Evolution

Abstract Developing earth‐abundant transition‐metal based materials to efficiently catalyze the oxygen evolution reaction (OER) is an urgent demand for electrochemical water splitting and rechargeable metal‐air batteries. Here, we developed a novel 3D hybrid electrocatalyst consisting of core‐shell structured CoS 2 /CoS 2 embedded into N‐doped carbon supported on electrochemically exfoliated graphene foil (EG/CoS 2 /CoS 2 ‐NC) by sulfurization treatment of EG/Co(OH) 2 /zeolitic imidazolate framework‐67 (ZIF‐67) as precursor. The thickness of the CoS 2 ‐NC shell derived from ZIF‐67 is 10 nm and the CoS 2 core generated from Co(OH) 2 nanosheet arrays has a particle size of ∼20 nm. Benefiting from the unique 3D core‐shell structure and synergistic effects, the EG/CoS 2 /CoS 2 ‐NC hybrid enormously promotes electrocatalytic OER activity with a low overpotential of 210 mV at a current density of 10 mA cm −2 and a small Tafel slope of 61.9 mV dec −1 . These values are far superior compared to the commercial Ir/C catalyst, and even better than other reported state‐of‐the‐art CoS 2 ‐based materials. In‐situ Raman spectroscopy together with ex‐situ XRD patterns reveal that the active centers of EG/CoS 2 /CoS 2 ‐NC hybrid are proven to be Co‐OOH species that are derived from Co−S groups during the OER process. The superb catalytic performance is also reflected in boosting electrochemical urea oxidation and hydrazine oxidation, where the accelerated oxidation reaction could be observed.