LAUSR

Abstract Hydrogen has been considered as one of the most promising renewable energy for production and storage. Here, we report an efficient method to synthesize MoS 2 -MoO 2 composite by hot-injection method using MoO 3 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 MoS 2 as well as MoO 2 . With increasing reaction temperature and time, oleic acid reorganizes the octahedral units of MoO 3 and gradually turn into low valence of Mo. After injecting S-precursor, OLA first reduces Mo-precursor to MoO 2 as core, and then S atoms replace O atoms to form MoS 2 as shell, eventually forming MoS 2 -MoO 2 core-shell structure. MoO 2 with few-layer MoS 2 can be observed by transmission electron microscope. A Tafel slope of 129 mV/dec is obtained for MoS 2 -MoO 2 composite, which is much better than MoS 2 and MoO 2 . The enhanced HER performance is attributed to the abundance active sites from MoS 2 and the improved charge transfer direction by MoO 2 .