Effects of nitrogen-doping structural changes of spherical hollow graphene on the growth of MoS2+x nanosheets and the enhanced hydrogen evolution reaction

Abstract MoS2, a two-dimensional (2D) layered structural transition metal dichalcogenide (TMDs), has been widely investigated towards hydrogen evolution reaction (HER) in previous few years. Except for the inert basal plane sites of the MoS2 itself, its inherent low conductivity also hinders the electron transfer process, which adversely affects its efficiency towards HER. Therefore, how to expose more edge active sites and at the same time improve the conductivity of MoS2, either intrinsically or with the help of high conductive substrates, is a key means to improve the HER performance of MoS2. Herein, the polystyrene (PS) nanospheres are used not only as an intercalation agent of graphene carbon sheets, but also as a spherical template for the preparation of 3D spherical hollow graphene. Different nitrogen precursors and nitrogen doping methods are used to prepare the 3D spherical hollow graphene substrate materials with different nitrogen-doping structures, such as amine N, pyrrolic N, pyridinic N or quaternary N. The investigation results show that the structure of doped nitrogen atom has a great influence on the loading of molybdenum disulfide. Among them, amine N was the most favorable for the loading of molybdenum disulfide, followed by pyrrole N, quaternary N and pyridine N. Moreover, the structure of doped N active sites synthesized by different preparation methods can also affect the uniform distribution of molybdenum disulfide on 3D spherical hollow graphene and the corresponding HER performance. The results show that, using ammonia as nitrogen source and PS microspheres as template, the prepared molybdenum disulfide loaded 3D spherical hollow graphene electrode material has the best HER performance, which should be attributed to the uniform distribution of the molybdenum disulfide and its close combination with the substrate, as well as the 3D spherical hollow structure. Moreover, the amorphous structure of molybdenum disulfide formed in the hydrothermal process can also improve the activity of HER.