Cobalt Sulfide Nanotubes (Co₉S₈) Decorated with Amorphous MoS_<i>x</i> as Highly Efficient Hydrogen Evolution Electrocatalyst

In this paper, we rationally designed a novel hybrid material consisting of Co₉S₈ nanotubes decorated with molybdenum sulfide lamellae (Co₉S₈/MoS_<i>x</i>), which was synthesized by consecutive solvothermal treatments. The extensive characterizations of the material using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM analyses certified that the decoration was amorphous MoS_<i>x</i>. The analysis of X-ray photoelectron spectra suggested the existence of a strong interface interaction between the two phases (Co₉S₈ and MoS_<i>x</i>). Subsequently investigated as an electrocatalyst for the hydrogen evolution reaction (HER) in acid media, the Co₉S₈/MoS_<i>x</i> hybrid exhibited a better activity than pristine MoS_<i>x</i> and Co₉S₈, requiring an overpotential of −161 mV to drive a current density of −10 mA cm^–2, as well as higher stability of the performance than Co₉S₈. Through experimental analysis, it was established that the improved HER activity and stability of the hybrid mainly resulted from the electrocatalytic synergistic effects between Co₉S₈ and MoS<sub><i>x</i>