Investigation Of MoS₂/RGO Nanocomposite Thin Films As Flexible Electrodes For Hydrogen Evolution Reaction

Hydrogen energy has been attracted a lot attention in that it is an ideal clean energy with high energy density,recyclability and little pollution.And it is expected to replace traditional fossil fuels,thus improving the ever-increasingly serious environmental pollution.Efficient and cheap electrocatalyst for hydrogen evolution reactions（HER）is the key to the development and utilization of hydrogen energy.Noble metal catalysts like Platinum（Pt）are commonly used in electrocatalytic hydrogen evolution reactions for their low overpotential（40 mV）and high reactivity.However,problems like small reserve and high cost limited the large-scale application.Therefore,it is of great significance to look for other efficient electrocatalysts for electrocatalytic hydrogen evolution reaction excluding noble metal catalysts.In recent years,molybdenum disulfide（MoS₂）nanomaterials has exhibited decent electrocatalytic capability,high catalytic activity and good stability in electrocatalytic hydrogen evolution reactions as well as abundant reserve.Nevertheless,the electrocatalytic capability of MoS₂ nanomaterials are influenced by the number of active site on the surface of S-Mo-S atomic layer and electron transport rate among atomic layer.In this paper,the reliable synthesis of MoS₂ with three different morphologies was achieved by hydrothermal method,and the effects of different morphologies and crystal quality on the electrocatalytic performance were also studied.Besides,the electron transport rate of MoS₂ were improved by the synthesis of reduced graphene oxide（RGO）and MoS₂ sheets composite.Meanwhile,the influences of MoS₂ loading capacity and annealing temperature on electrocatalytic performance were investigated and obtained the flexible MoS₂/RGO composite film with excellent electrocatalytic capability.The research content of this paper can be concluded into three parts as following:1.Reliable synthesis of MoS₂ nanostructures with different morphologies was carried out in detail.Firstly,the precursor powder——（NH4）2MoS4 was synthesized by the reaction between（NH4）6Mo7O24·4H2O and（NH4）2S solution.Since the precursor（NH4）2MoS4 contains both Mo and S,the atom ratio of Mo and S is fixed in the hydrothermal reaction,which can exclude the interference of Mo:S ratio disorder in the study of electrocatalytic performance for different MoS₂ structures.Besides,the effects of temperature,precursor concentration,reaction time and solvent ratio（DMF:H2O）on the MoS₂ morphologies and crystallinity were detailed investigated,achieving the controlable synthesis of three different MoS₂ nanostructure（quantum dots,nanosheets and nanoflowers）.2.Study of electrocatalytic performance for different MoS₂ nanostructures by electrochemical tests equipped with three electrodes.The glassy carbon electrode which was loaded with certain amount of MoS₂ nanostructures,platinum wire electrode and Ag/AgCl electrode were served as working electrode,reverse electrode and contrast electrode,respectively.The corresponding overpotential of quantum dots,nanosheets and nanoflowers were 410 mV,310 mV and 365 mV,while the Tafel slope were 228.2 mV/dec,32.7 mV/dec and 92.16 mV/dec.It turns out that the electrocatalytic capacity of nanosheets is the highest among the three MoS₂ nanostructures.In addition,it can be concluded that nanosheets have the best electrocatalytic performance due to the better crystallinity,larger specific surface and good electronic transport channels from the analysis of XRD and TEM characterization.3.Synthesis of graphene oxide（GO）by Hummer method and synthesis of MoS₂/RGO composite film by vacuum filtration method and thermal reduction.The influences of conductivity and MoS₂ loading amount on the electrocatalytic performance of MoS₂/RGO composite film were studied by adjusting the MoS₂ loading amount and reduction temperature.It was found that the conductivity of MoS₂/RGO composite film increased with the increase of annealing temperature.Meanwhile,the conductivity firstly decreases and then increase with the increase of MoS₂ loading amount.Under annealing temperature of 700℃,the composite film exhibits the best electrocatalytic hydrogen evolution activity with stable electrocatalytic behavior.The overpotential and Tafel slope are 237 mV and112 mV/dec,respectively.Furthermore,the electrocatalytic hydrogen evolution performances of the MoS₂/RGO composite film under different bending angles were also investigated.It turns out that MoS₂/RGO composite film can keep relatively high electrocatalytic hydrogen evolution activity when the bending angles range from 0° to 90°,which lays the foundation of design of new flexible electrocatalytic devices.