MoS 2 -MoO 2 composite electrocatalysts by hot-injection method for hydrogen evolution reaction

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 .