Electrochemical Fabrication And Hydrogen Evolution Catalytic Properties Of Amorphous Molybdenum Sulfide Films

In the face of the global's energy and environmental crises,the development of renewable and clean energy technology has become urgent.Hydrogen is regard as a very important clean energy,which owns a high energy density and products the only one kind of pollution-free product,water,during the combustion and release of energy.Since hydrogen is not a natural energy source,the development of efficient hydrogen production technology becomes the focus of research in this field.Compared with steam methane reforming and coal gasification,which rely on fossil fuels and cause environmental pollution,producing hydrogen by water electrolysis is a promising green technology.According to a large number of researches on hydrogen evolution electrocatalysts in recent years,it is found that platinum is the best hydrogen evolution electrocatalyst at present.However,it is rare and expensive that platinum is a precious metal,which limits its wide application.Therefore,it is important to research the non-noble metal catalysts.MoS₂ is a well-know promising electrocatalytic material for hydrogen evolution reaction?HER?.Nevertheless,the commonly used preparation methods are harsh to experimental conditions,generally requiring high temperature,lengthy duration,and usually involving the use of toxic reagents.The electrochemical deposition is a simple and feasible method to prepare materials.In this paper,molybdenum sulfide materials were prepared by the cyclic voltammetry and potentiostatic electrochemical deposition method.The main contents and conclusions are as follows:?1?Molybdenum sulfide films were prepared on titanium sheet or carbon cloth by cyclic voltammetry method in the three electrode system.Through using the linear sweep voltammetric curve to compare the effects of different electrodeposition parameters?potential range,scanning speed,time,the concentration of potassium chloride?on hydrogen evolution activities of films,the best electrodeposition parameters have been chosen.It is as fallows:the electrolyte solution is 2 mM?NH₄?₂MoS₄ in 0.1 M KCl aqueous solution.The potential range is 0.4¹.3 V.The number of CV is 30 cycles.Scanning speed is 20 mv/s.The samples prepared in the best conditions were characterized by XRD,SEM and XPS.The results show that the surface of the prepared film is uniform and dense,and is formed by the compact accumulation of nanoparticles with a diameter of 50¹00 nm.The thickness of the thin film on the titanium sheet and carbon cloth support is about 400 nm and 50 nm respectively.The sample is composed of amorphous MoS₂ and MoS₃ mixture thin film,in which the chemical formula of MoS₃ can be considered as[Mo?IV??S₂?^2-S^2-].the hydrogen evolution activities was tested in 0.5 M H₂SO₄ solution,including linear sweep voltammetry,double-layer capacitance and stability.The results showed that the MoS_x films prepared on the titanium sheet owned an overpotential of²04 mV?vs RHE?at a current density of-10 mA cm^-2,a Tafer slope of 44 mV decade^-11 and C_dll of 6F cm^-2.The MoS_x films prepared on the carbon cloth had an overpotential of 180 mV?vs RHE?at a current density of-10 mA cm^-2,a Tafer slope of 46 mV decade^-11 and C_dll of 8 F cm^-2.The MoS_x thin films prepared by cyclic voltammetry electrochemical deposition method have good stability in acid medium.?2?Molybdenum sulfide films were prepared on titanium sheet or carbon cloth by Potentiostatic method in the three electrode system.Through using the linear sweep voltammetric curve to compare the effects of different electrodeposition parameters?potential and time?on hydrogen evolution activities of films,the suitable electrodeposition parameters have been selected.It is as fallows:the electrolyte solution is 2 mM?NH₄?₂MoS₄ in 0.1 M KCl aqueous solution.The potential is-1.4 V.The time is 60 min.The samples prepared in the suitable conditions were characterized by XRD,SEM and XPS.The results show that the surface of the prepared film is rough,and appears obvious granular with cracks.The thickness of the thin film on the titanium sheet and carbon cloth support is about 300 nm and 200 nm respectively.The sample is composed of amorphous MoS₂ thin film.The hydrogen evolution activities was tested in 0.5 M H₂SO₄ solution,including linear sweep voltammetry,double-layer capacitance and stability.The results showed that the MoS_x films prepared on the titanium sheet owned an overpotential of¹98 mV?vs RHE?at a current density of-10 mA cm^-2 and a Tafer slope of 48 mV decade^-1.C_dl is 10.7 F cm^-2.The MoS_x films prepared on the carbon cloth had an overpotential of 167 mV?vs RHE?at a current density of-10 mA cm^-2,a Tafer slope of 49mV decade^-1 and C_dl of 31.6 F cm^-2.The stability of MoS₂ thin films prepared by potentiostatic electrochemical deposition is poor in acid medium.