Hierarchical Amorphous Carbon-Coated Co/Co₉S₈ Nanoparticles on MoS₂ toward Synergetic Electrocatalytic Water Splitting

The development of electrocatalysts with excellent performance, affordable price, and abundant reserves is an important way to realize the overall water splitting. In this study, we design a unique preparation process to form a carbon-coated Co/Co₉S₈–MoS₂ bifunctional catalyst. Excessive H₂S generated in the decomposition process of ammonium thiomolybdate can partially sulfurize carbon-coated Co nanoparticles, and Co/Co₉S₈ mixed phases will be formed on MoS₂. The as-prepared catalyst possesses good bifunctional electrocatalytic activity under the alkaline environment for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The amorphous carbon-coated Co/Co₉S₈–MoS₂ composite shows a low overpotential of 128 mV for HER and 325 mV for OER in 1 M KOH solution, respectively. Besides, the amorphous carbon shell can prevent Co/Co₉S₈ nanoparticles from corrosion, and the catalyst shows remarkable long-term cycle stability.