Hydrogen Evolution Properties Of Transition Metal Sulfide Composite Nanomaterials

With the development of the urbanization and industrialization,the energy shortage,environmental pollution and other problems caused by the excessive use of fossil energy are becoming more and more serious.During the process in the burning of fossil energy,the greenhouse gases such as the carbon dioxide will be discharged,leading to the global warming,acid rain,haze and other environmental problems.Therefore,the sustainable development of human society needs the clean and renewable energy to replace the fossil energy.The hydrogen energy has the advantages of the zero pollution of reaction products,convenient transportation,convenient storage and abundant sources,etc.It widely applied and could be used as a good alternative energy to the fossil energy.The hydrogen production by the electrolysis of water is an industrial hydrogen production method with the simple equipment,no pollution and high purity.However,the main problems limiting the development of hydrogen production from the electrolytic water lie in the high cost of preparation of catalyst electrode,the large amount of synthetic catalystuse,the low efficiency of hydrogen production,the low dynamic strength of the substrate material and catalyst,and the poor conductivity and other problems.The Pt-based catalyst is an ideal catalyst for the highly efficient hydrogen evolution.However,the resource scarcity and higher cost of precious metals have limited development.Therefore,it is particularly very important and is the research significance of practical application to study the hydrogen evolution catalyst with the low cost,high efficiency and high stability.Nickel foam is widely used as an electrode substrate as a good conductive substrate.Non-precious metals such as transition metals,with underfilled electronic structures are conducive to the formation of adsorption bonds.It can get better hydrogen evolution performance.The NiMoO₄,CoMoO₄,Ni_0.5Co_0.5MoO₄ nanosheet arrays?NSAs?precursors have been synthesized by the hydrothermal method on the nickel foam substrates.And then the three transition metal composite nanosheet arrays of NiS₂/MoS₂,CoS₂/MoS₂,NiS₂/CoS₂/MoS₂ are obtained by the vapor deposition sulfurization.Among them,the electrocatalytic activity of NiS₂/CoS₂/MoS₂ nanosheet arrays is the best,which can be attributed to large number of exposed active sites and multiple heterogeneous interfaces.In the 1M KOH electrolyte solution,when the current density is 10 mA·cm^-2,the overpotential is 112 mV.The slope of Tafel is 59 mV·dec^-1.The current density does not change basically after the CV cycles of 2000 times.When the fixed overpotential is 112mV,the hydrogen can be produced continuously and stably for more than 40 h.The effective composite growth of transition metal sulfide nanomaterials on the nickel foam substrates has been completed by this work,and the efficiency of electronic transmission has been increased.By comparing the bimetal and trimetal sulfide,the more heterogeneous interfaces between the components can be clearly explicated,and the performance of transition metal hydrogen-evolution catalyst can be improved.The Ni_0.8Co_0.2MoO₄ nanowire arrays?NWAs?precursor has been successfully prepared on the nickel foam,and then which is converted into the NiS₂/MoS₂/CoS₂transition metal composite nanowire arrays by means of the gas phasesulfide and in situ reaction.When the current density is 10 mA·cm^-2 in the 1 M KOH electrolyte solution,the overpotential is 62 mV respectively.The slope of Tafel is 70 mV·dec^-1.After the cycles of 2000 times,the current density is basically unchanged.When the fixed overpotential is169 mV,the hydrogen can be produced continuously and stably for more than 18 h.The larger surface area structure is provided by the NiS₂/MoS₂/CoS₂ nanowire arrays layered and branchedon the nickel foam.The transfer of electron from the Ni and Co to the Mo is causedby the synergistic effect of the NiS₂/MoS₂,CoS₂/MoS₂ and NiS₂/CoS₂ hybrid interface,and there is a slight structural disorder in the multilayer MoS₂,as the electrocatalytic active center of alkaline HER,it has effectively improved the hydrogen evolution performance.By changing the reagent and condition,the CoMoO₄ nanometer flower arrays?NFAs?synthesized by the hydrothermal method on the nickel foam substrate is used as the precursor.After the sulfidation,the nanosheet on the surface of nanometer flower arrays is changed into the pieces composed by the rough nanoparticles,the CoS₂/MoS₂nanometer flower arrays is obtained.In the 1 M KOH electrolyte solution,when the current density is 10 mA·cm^-2,the overpotential is 50 mV,and the slope of Tafel is 76mV·dec^-1.After the cycles of 2000 times,there is a good durability shown still in the alkaline medium,and the stability is maintained after the continuous hydrogen evolution for the 70 h when the overpotential is 100 mV.There is enough space between the 3D nanometer flowers network structures,to efficiently diffuse the electrolyte inward and release hydrogen bubbles outward,the process of the electrolyte diffusion inward and hydrogen gasbubblesreleaseoutward can be realized efficiently.