Preparation Of Transition Metal Sulfide Composites And Study On Their Photoelectrochemical Hydrogen Evolution Properties

In recent years,the massive use of fossil energy has caused various environmental problems around the world.As one of the important members of clean energy,hydrogen energy,with its high calorific value and zero carbon emission,has gained great attention in the past few years.Novel hydrogen production and storage technologies have become hot research topics.In addition to industrial processes that rely on fossil fuels,photochemical decomposition of aquatic hydrogen is an economical and green production pathway.Metal sulfide semiconductors,including MoS₂,CdS,Cu₂S,SnS₂,etc.,have been widely studied in the field of photocatalysis and photocatalytic hydrogen evolution due to their controllable structure and excellent catalytic properties.However,there are still many problems that limit the further development of photoelectrochemical hydrogen evolution,such as the narrow light absorption range of most of the semiconductors currently used for photoelectrochemical hydrogen evolution;the electrons generated by the semiconductor after absorbing light energy are easily compounded with the holes remaining in the valence band;the small number of electrons effectively involved in the interfacial redox reaction;and the slow interfacial reaction kinetics;the small number of electrons effectively involved in the interfacial redox reaction;and the slow interfacial reaction kinetics.In this thesis,the above limiting steps are optimized to enhance the photoelelctrocatalytic hydrogen precipitation performance of transition metal sulfides,respectively,with the following main components:（1）Expanding light absorption range and accelerating electron transfer.Reduced graphene oxide loaded CuS composites（RGO-CuS）were obtained by hydrothermal method.RGO has good electrical conductivity,which can effectively reduce the interfacial charge transfer resistance of the composites and accelerate the electron transfer process.Meanwhile,the transition metal sulfide CuS has a suitable band gap and conduction band position,which can effectively absorb NIR light to complete the reduction of hydrogen protons.Therefore,the composite exhibits excellent photocatalytic hydrogen precipitation performance under NIR light,and the performance of RGO-CuS does not deteriorate significantly after 5000 cycles in acid,showing good durability.（2）Promoting electron-hole separation and acceleratling electron transfer.Polyaniline（PANI）-loaded transition metal sulfide SnS₂ hexagonal nanosheets（PANI/SnS₂）were prepared by hydrothermal and hybrid methods.PANI and SnS₂ exhibit photothermal conversion ability under NIR light irradiation,so NIR light irradiation can effectively increase the interfacial temperature of the materials.The increase of the local temperature will accelerate the electron transfer process and promote the interfacial catalytic reaction.Therefore,the composites not only exhibit superior electrocatalytic hydrogen precipitation performance under NIR light irradiation.Meanwhile,the heterojunction formed by PANI and SnS₂ can effectively promote electron-hole separation,so the composites also exhibit superior electrocatalytic hydrogen precipitation performance.（3）Enhancement of photoabsorption,promotion of electron-hole separation,acceleration of electron transfer and acceleration of interfacial hydrogen precipitation reaction kinetics.The snowflake-like transition metal sulfide Cu₂S/MoS₂/Pt heterostructures were constructed by two-step hydrothermal and electrodeposition methods.p-n heterojunctions and Schottky junctions formed between Cu₂S/MoS₂/Pt can effectively promote efficient electron-hole separation.And MoS₂ exhibits superior photothermal conversion ability under NIR light irradiation,which can effectively increase the interfacial temperature of the composites under NIR light irradiation,thus reducing the interfacial charge transfer resistance of the composites and promoting the interfacial catalytic reaction.Therefore,the composites exhibit not only superior electrocatalytic hydrogen precipitation performance under NIR light irradiation but also superior photocatalytic hydrogen precipitation performance.The electrocatalytic and photocatalytic hydrogen precipitation properties of the composites were further improved after loading Pt nanoparticles.（4）Expanding light absorption range,enhancing light absorption,promoting electron-hole separation,and accelerating interfacial hydrogen evolution reaction kinetics.The high interfacial charge transfer resistance of lightly doped SiNWs was overcome by loading gold nanoparticles onto the surface of narrow bandgap material silicon nanowire arrays（SiNWs）by chemical deposition,thus breaking the dilemma of difficulty in constructing SiNWs-based composite structures by electrodeposition.Subsequently,the transition metal sulfide CoS was loaded onto the SiNWs/Au surface by a convenient electrodeposition method.CoS with abundant hydrogen precipitation active sites and excellent optical transparency as a co-catalyst can promote the hydrogen production activity of the SiNWs photocathode,while the unique localized surface plasmon resonance effect（LSPR）of Au further promotes light absorption.The obtained core-shell structures exhibit excellent photocatalytic hydrogen precipitation performance under the irradiation of simulated solar light.Meanwhile,the SiNWs/Au/MoS₂ and SiNWs/Au/Ni₃S₂ constructed by electrodeposition also exhibit excellent photocatalytic hydrogen precipitation activity.