MoS₂-MoO₂ composite electrocatalysts by hot-injection method for hydrogen evolution reaction

Hydrogen has been considered as one of the most promising renewable energy for production and storage. Here, we report an efficient method to synthesize MoS₂-MoO₂ composite by hot-injection method using MoO₃ and S powder as precursors with oleic acid (OA) and oleylamine (OLA) as solvent, respectively. The X-ray diffraction shows the presence of the peaks from both MoS₂ as well as MoO₂. With increasing reaction temperature and time, oleic acid reorganizes the octahedral units of MoO₃ and gradually turn into low valence of Mo. After injecting S-precursor, OLA first reduces Mo-precursor to MoO₂ as core, and then S atoms replace O atoms to form MoS₂ as shell, eventually forming MoS₂-MoO₂ core-shell structure. MoO₂ with few-layer MoS₂ can be observed by transmission electron microscope. A Tafel slope of 129 mV/dec is obtained for MoS₂-MoO₂ composite, which is much better than MoS₂ and MoO₂. The enhanced HER performance is attributed to the abundance active sites from MoS₂ and the improved charge transfer direction by MoO₂.