| With the development of renewable energy such as wind energy,tidal energy and light energy,these energy sources have inherent characteristics of uncentralization,intermittency and unpredictability,which restrict their full use.Because hydrogen has the characteristics of clean,high energy density and no discharge of pollutant,these renewable energies can be used more widely if converted to hydrogen to storage.Hydrogen was produced from the water electrolysis;the renewable energy provides the volatile electrical energy.Water electrolysis requires electricatalyst to increase its reaction rate,and then to enhance the conversion efficiency of the renewable energy.At present,the best electrocalysts are Pt-based the nobel metal catalyst.But this kind of catalyst were restricted in large-scale application due to the high cost and the scarcity,therefore,it is necessary to research and develop cheap and efficient electric catalysts to replace Pt-based catalysts.It has been found that molybdenum disulfide(MoS2)has catalytic activity and its marginal sites are the catalytic activity site.And the adsorption free energy of hydrogen atoms on MoS2 is very close to the adsorption free energy of hydrogen atom on Pt,which provides the theoretical principle of the high effective hydrogen evolution reaction catalyst of MoS2,and is priority studied as an efficient catalyst.Nano MoS2 is a semiconductor material with two-dimensional laminar structure,and the catalytic activity site of hydrogen evolution reaction is located on the edge of laminated structure,so that it is necessary to study and prepare MoS2 with a large number of active sites and the ability to transmit electrons quickly.In addition,the catalytic hydrogen evolution reaction form an electron transfer process from conductive substrate and catalyst to electrolyte,and another process of the ions conversion on interface between the catalyst and electrolyte.The catalytic efficiency is influenced by two processes.If the conductive substrate and catalyst as a whole will be considered as a catalytic electrode,the two processes above will be treat as the transformation process of the electron and ions between the catalytic electrode and the electrolyte.It is necessary to study and prepare the catalytic electrode with the properties of electron and ions conversion easily.In this paper,basing on understand fully the characteristics of MoS2 catalytic activity and electrode,a variety of strategies for the regulation of catalytic activity are adopted,and assembled the three-dimensional efficient electrode.MoS2 catalytic activity regulated by different angles,such as active site regulation,conductivity regulation,interlayer doping and in-plane doping.And the three-dimensional electrode was assembled through combining catalysts and the conductive matrix.By the electrochemical to analysis the catalytic activity,the results demonstrated that the catalytic performance of catalysts were obviously impoved by the regulation of active site,conductivity and interlayer doping,and the catalysts from the way of in-plane doping not only improve the catalytic activity of hydrogen evolution reaction,but also exhibit the performance of oxygen evolution reaction.The specific research contents of this paper include the following aspects:(1)The catalytic activity of MoS2 is located at the edge of the lamellar,and exposure to active sites as much as possible is one of the means to improve catalytic activity.Molybdenum disulfide with defect sites is prepared by hydrothermal method,and then a kind of MoS2 catalyst can be obtained by the ultrasonic exfoliation and centrifugation of MoS2 with defect sites,which the obtained catalyst can disperse steadily in water for long time.The catalyst is characterized by SEM,TEM.XRD and XPS.it is found that the structure of catalyst is the MoS2 nano-dot modified on the nanosheets.Through the characterization of electrochemical test,the Tafel slope of MoS2 prepared by hydrothermal method is 118 mV dec-1,the catalysts of MoS2 nandots modified nanosheets exhibited a low Tafel slope for 57 mV dec-1.Furthermore,by cyclic voltammetry under different scan rate to calculate the capacitance value,the capacitance value of MoS2 nanosheet modified by nanodots is twice more than the capacitance value of the defect-rich MoS2,which demenstated that MoS2 nanodots modified nanosheets have the higher catalytic activity,and greatly increases the number of the catalytic active sites.And the electrochemical stability of MoS2 nanodots modified nanosheets is tested by chronoamperometry,and the catalyst shows high catalytic stability in 10 hours for the test.(2)The regulation of the MoS2 conductivity was studied.A simple hydrothermal method was used to grow the MoS2 on the carbon fiber paper with the three-dimensional structure,and achieved a three-dimensional electrode,and then immersing the electrode in the n-hexane solution containing n-butyllithium.Through characteristing the composition and structure of the electrode and catalyst by SEM,TEM,XRD,XPS and Raman,it is can find that the on the carbon fiber surface is nanoparticles.And the crystal structure of MoS2 is converted from the semiconducting 2H phase to metallic IT phase after immersing,which is due to intercalating Li ions into MoS2 interlayers.Besides,the band structure and density of states of MoS2 before and after Li ions intercalation were calculated by density functional theory,the results show that band gap of MoS2 disappears after intercalating Li ions,it is also confirmed that MoS2 has the metallicity after intercalating.The catalytic performance of three-dirnensional electrode before and after iminersing was tested,the Tafel slope of the electrode were reduced from 70 mV dec-1 to 62 mV dec-1 after Li ions intercalating.Especially,the overpotential of the electrode become more low form 228.2 mV to 115.6 mV at the current density of 10 mA cm-2 after Li ions intercalating.These results demonstrated that the catalytic activity of electrode was impoved greatly after Li ions intercalating.The stability of the catalyst is tested by chronoamperometry,which also shows that the three-dimensional electrode after Li ions intercalating maintained the stable catalytic performance.(3)The regulation of the MoS2 interlayer doping was studied.A three-dimensional electrode were assembled by the hydrothermal method to load the catalyst on the carbon fiber paper,using a precursor solution introducing tungsten source of the prepared MoS2.In order to fully explain the difference of catalytic performance before and after doping,the different electrodes are obtained in the different solution by controlling proportions of precursor.The structure and composition of different eletrodes and catalysts are characterized by SEM,TEM,XRD.XPS,Raman,the results show that the different catalytic electrodes were assembled by this method and the catalyst on the surface electrode have the different morphological structure.The composite catalyst of MoxW1-xS2 were uniformly loaded on the carbon fiber paper when the ratio of molybdenum source to tungsten source is 3:1.The energy band and density of state of the heterogeneous formed by MoS2 and WS2 were calculated by density functional theory.The heterogeneous structure has a smaller band gap of 1.470 eV.The hydrogen evolution catalytic performance of the different electrodes is tested.The results show that the composite catalysts have higher catalytic activity,especially MoxW1-xS2/CFP(3:1)show the best catalytic performance,its Tafel slope is 75 mV dec-1.The stability of the catalyst is tested by chronoamperometry;the results shows that the three-dimensional electrodes of Moxw1-xS2/CFP(3:1)have good catalytic stability.(4)The regulation of the MoS2 in-plane doping was studied.A three-dimensional electrode were assembled by the hydrothermal method to load the catalyst on the carbon fiber paper,using a precursor solution introducing cobalt salt of the prepared MoS2.Meanwhile,the different electrodes are assembled in the solution containing the different precursor.The structure and composition of different eletrodes and catalysts are characterized by SEM,TEM,XRD and XPS,the results show that the different morphological electrodes were assembled by using the different precursors,moreover,the composite catalyst of MoxCo1-xS2 were uniformly loaded on the carbon fiber paper when molybdenum salt and cobalt salt exist in the solution at the same time.The energy band and density of state of MoS2 with a Mo atom replaced by Co atom were calculated by density functional theory.The results show that the Co doped MoS2 shows the conductor properties.The electrolytic water catalytic performance of the different electrodes is tested in an alkaline environment.The results show that the hydrogen evolution catalytic performance of MoS2 was improved after Co-doped,and the prepared MoxCo1-xS2 catalysts show the efficiently catalytic performance of oxygen evolution reaction.The Tafel slope of hydrogen evolution reaction and oxygen evolution reaction is 74 mV dec-1 and 78 mV dec-1 respectively.The stability of the catalyst is tested by chronoamperometry,the results show that the three-dimensional electrode has excellent catalytic stability for hydrogen evolution reaction and oxygen evolution reaction. |
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