Preparation, Characterization And Electrochemical Ppropertypropertyproperties Properties Of Molybdenum Disulfide/graphene

Energy crisis has gradually attracted the world’s attention due to the mismatch between the severe consumption of traditional fossil fuels and its daily declining availability associated with the environment pollution during the energy-conversion process in the 21 st century. Recently, Transition metal sulfides（TMS） have been triggered as novel two dimensional materials which are widely used in many applications, especially in the direction of hydrogen evolution reaction（HER） catalysts due to their unique chemical and physical properties. Among the families of TMS, Molybdenum disulfide（MoS₂） has exhibited great potential in HER performance. However, MoS₂, a typical semiconductor, shows extremely low conductivity which is not advantageous in HER performance. Therefore, a novel strategy about the catalyst should be designed not only in creating more active sites but also in improving the conductivity of the catalyst. Inspired by the advantages mentioned above, we have successfully synthesized MoS₂/reduced graphene oxide（MoS₂/rGO） composites, resulting in excellent HER performance through various strategies. The detail work can be briefly summarized as follows:1. Three-dimensional MoS₂/rGO hydrogel as active catalyst for hydrogen evolution reaction has been synthesized through one-step facile hydrothermal method. A certain concentration of graphene oxide（GO） suspension could be transferred into three-dimensional graphene hydrogel through hydrothermal process, which leads to the enlarged surface area. Moreover, the as-prepared hydrogel exhibits excellent stability when used in many applications, such as biosensor, catalysts, energy-storage device and so on, since the 3D network structure can effectively prevent the volume change during the long time stability. The other hand, graphene can prohibit the MoS₂ nanosheets from stacking along the 002 crystal planes, which means lower layer resistance and more additional active sites. We here combine a certain amount of precursors with different GO suspensions. The MoS₂/r GO3 with the GO suspension of 1.5 mg/mL shows an superior HER performance with a small onset overpotential of 125 mV, Tafel slope of 41 mV/decade, extremely high double layer capacitance of 29.6 mF/cm2, and outstanding stability performance even after 1000 th continuous tests.2. The three-dimensional（3D） O-incorporated MoS2/rGO composite for improved hydrogen evolution reaction has been synthesized through one-step solvent assisted hydrothermal method. Previous work confirms that the active sites stemmed from the edges of 002 crystal planes rather than the inert basal planes. Therefore, one of the most effective ways to improve the HER catalytic activity is to fabricate rich active sites. In addition, another key factor to better the HER performance should focus on improving the conductivity of the catalysts. From such consideration, an advanced MoS₂ HER catalysts should be carefully designed to create more active sits as well as improving the conductivity of the catalyst. In order to unite the two mentioned strategies together, we have proposed and designed O-incorporated MoS₂/r GO composites as superior catalysts for HER. Here, the incorporated oxygen actes key roles not only in engineering the disorder process, leading to the rich active sites, but also in improving the intrinsic conductivity. In addition, controlled experiments reveal that the incorporated oxygen comes from the solvent N, N-Dimethylformamide（DMF）. Further work confirms that DMF has huge influence in adjusting the morphologies of the as-obtained composites. Due to the successful incorporation of oxygen into MoS₂ nanosheets, the O-incorporated MoS₂/r GO composites show an competitive onset overpotential as small as only 103 mV/decade, a small tafel slope of 43 mV/decade, a large current density of 15 mA/cm2 at the overpotential of 200 mV, noly 1.7% HER activity lost even after 2000 th continuous cycles in acid media, and a large Turnover frequency value of 2.34 S-1 at an overpotential of 250 mV. Moreover, the value of double layer capacitance for O-incorporated MoS₂/rGO is more than 11.2 times lagrer than that of undoped MoS₂/rGO.