Investigation On The Preparation Of Transition Metal Sulfides And Their Electrocatalytic Properties For Hydrogen Evolution Reaction

With the increase of population and energy consumption,the energy crisis has become the focus of the world.The development of sustainable and renewable energy?e.g.wind,solar and hydrogen energies?is the most effective way to solve the energy and environmental problems.Hydrogen energy has attracted much attention due to its advantages of high combustion calorific value,no pollution,and abundant sources.At present,the electrocatalytic hydrogen production is the most efficient method for hydrogen production.There are two kinds of electrocatalysts for hydrogen evolution reactions?HER?,such as noble metal electrocatalyst and non-noble metal electrocatalyst.Due to the high price and the scarcity of reserves,the large-scale applications of noble metal electrocatalysts have been greatly hindered.The transition metal sulfides,as an example of non-precious metal electrocatalysts,have great potential in field of electrocatalytic HER due to their low price and abundant reserves.However,the HER properties of transition metal sulfide electrocatalysts are still far lower than those of noble metal electrocatalysts,and there are also some problems existed,such as poor conductivity and inherent agglomeration.According to the above problems,this dissertation aims to improve the HER properties of transition metal sulfides?FeS₂ and Cu₂MoS₄?through intercalation of heterogeneous atoms and hybridization with highly conductive graphene.The main results are summarized as below.?1?Pyrite FeS₂ nanoparticles have been prepared using hot injection method in Schlenk system.After a series of explorations of the experimental conditions,such as adding surface agent,changing sulfur source,and changing reaction temperature,it is found that pyrite FeS₂ can be prepared using sulfur powder as sulfur source under the reaction temperature of 220?.The microstructures and morphologies of pyrite FeS₂are further characterized and analyzed.?2?A series of Fe_1-xCo_xS₂/RGO hybrid electrocatalyst are successfully prepared by hot injection method.The microstructures,morphologies and electrochemical properties are systematically investigated.The results show that Fe_0.39Co_0.61S₂/RGO hybrid electrocatalyst exhibits the best HER performance,as indicated by lower overpotential of 198 mV(10 mA cm^-2)and smaller Tafel slope of 94 mV dec^-1.The enhanced HER activity might be owing to the synergistic effects between the highly conductive RGO and the electroactive Fe_0.39Co_0.61S₂.Moreover,the HER mechanism is further explained by density-functional calculations.The results indicate that the introducing of Co atoms into FeS₂ electrocatalyst can modulate the adsorption behaviors of hydrogen atom with a smaller Gibbs free energy close to zero,which can provide beneficial theoretical supports for the experimental results.?3?Taking Cu₂O as the template,Cu₂MoS₄ nanosheets and three types of Cu₂MoS₄/RGO nanosheets with different concentrations of RGO?Cu₂MoS₄/RGO-10%,Cu₂MoS₄/RGO-25%and Cu₂MoS₄/RGO-50%?have been successfully prepared by hydrothermal method,which are further characterized by XRD,SEM,TEM,Raman and electrochemical measurements.The results show that Cu₂MoS₄/RGO-25%electrocatalyst exhibits the best HER performance.Compared with Cu₂MoS₄ nanosheets,the overpotential and Tafel slope of Cu₂MoS₄/RGO-25%electrocatalyst decrease significantly.Moreover,the linear sweep voltammetry?LSV?curve of Cu₂MoS₄/RGO-25%electrocatalyst almost does not change after 1000 cyclic voltammetry?CV?cycles.This indicates that Cu₂MoS₄/RGO-25%electrocatalyst has excellent HER performance and good cycling stability.