Preparation Of Self-supported Transition Metal Chalcogenide Catalysts And Their Performance Of Overall Water Splitting

The research and development of renewable and clean energy is of great significance to solve the serious energy crisis and environmental pollution owing to excessive consumption of fossil fuels.Hydrogen energy（H₂）is considered as a potential new energy to replace fossil fuels due to its high energy density,renewable and environment-friendly advantages.Among numerous hydrogen production methods,electrocatalytic overall water splitting（OWS）is an important way to obtain hydrogen energy effectively,which consists of anodic oxygen evolution reaction（OER）and cathodic hydrogen evolution reaction（HER）.However,these two reactions are multi electron transfer processes with slow kinetics,so it is necessary to reduce the reaction energy barrier with the help of catalyst.Moreover,so far,the efficient OER and HER catalysts are still precious metal materials such as Ru O₂/Ir O₂ and Pt respectively,but the high price and scarce reserves seriously restrict their large-scale industrial application.Therefore,the exploration of low-cost,efficient,stable,and abundant non-precious metal catalysts plays a vital role in developing water electrolysis hydrogen production technology and alleviating energy and environmental problems.This thesis aims to study the controllable preparation of self-supported transition metal chalcogenide catalysts,and optimize the OER,HER and OWS properties of the catalysts through a series of strategies such as carbon material coating,morphology and structure regulation,component regulation,heterostructure construction,interface electronic regulation and combination with conductive substrate.The research contents of this paper are as follows:（1）In view of the unsatisfactory conductivity and HER performance of transition metal oxides（TMOs）,the promotion effect of reduced graphene oxide（r GO）coating on the OWS performance of TMOs was explored.In this paper,the r GO encapsulated CoNiO₂ nanosheet array catalyst in-situ grown on foam nickel（NF）（CoNiO₂@r GO/NF）was prepared by hydrothermal method and annealing treatment.The sheet-on-sheet structure composed of CoNiO₂ and r GO shows effective synergistic coupling effect,which not only improves the conductivity and activity of the catalyst,but also can maintain the stability of the structure,thus significantly improving the OER and HER performance.In addition,the self-supported structure formed by combining with the conductive substrate NF can further improve the conductivity,increase the active sites,promote the release of bubbles,and further enhance the catalytic activity and stability.In 1.0 M KOH solution,the OWS electrolytic cell constructed with CoNiO₂@r GO/NF as a bifunctional catalyst only needs a potential of 1.56 V to achieve a current density of 10 m A·cm^-2 and can operates stably for more than 40 hours.（2）In view of the unsatisfactory OER performance of transition metal sulfides（TMSs）,the optimization effect of component regulation on the OWS performance of TMSs was explored.In this paper,three dimensional（3D）porous Ni-Fe-S/NF nanosheet arrays catalyst was prepared by hydrothermal method.The Ni₃S₂-Fe S/NF-2 catalyst obtained through component regulation has optimized 3D porous nanosheet structure and electronic structure,which can effectively optimize the adsorption energy of reaction intermediates,increase specific surface area and active sites,and promote the electrochemical reaction.Therefore,Ni₃S₂-Fe S/NF-2 exhibits excellent OER and HER performance.For OWS,it only needs potentials of 1.55 and 1.75 V to reach 10 and 100 m A·cm^-2 respectively,and it can work stably for at least 100 hours.（3）In view of the problem that TMSs are easily oxidized and thus cause reduced stability in alkaline and oxidative environments,the synergistic effect of morphology regulation and heterostructure construction on the OWS performance of TMSs was explored.In this paper,a hierarchical heterostructure nanoarray catalyst was prepared through hydrothermally hybridizing NiMo O₄ nanosheets with NiCo₂S₄ nanotubes（NiCo₂S₄@NiMo O₄/NF）.This unique self-supported hierarchical structure not only inherits the advantages of integrated electrode like fast charge transfer,abundant active sites,and high stability,but also combines the specialty of NiCo₂S₄ and NiMo O₄ in HER and OER,respectively.In addition,heterostructure can also regulate the electronic structure of the catalyst,optimize the adsorption/desorption energy of reaction intermediates,and generate strong electronic coupling and synergistic effect,thus effectively improving OER and HER performance of catalyst.NiMo O₄ can also prevent the NiCo₂S₄ from oxidation failure and effectively enhance the catalytic stability.For OWS,NiCo₂S₄@NiMo O₄/NF only requires potentials of 1.46,1.63and 1.75 V to reach 10,50 and 100 m A·cm^-2 respectively,and it can operate stably at these potentials for over 100 hours.（4）In view of the instable OER performance of transition metal selenides（TMSes）in alkaline and oxidative environments,the synergistic effect of heterostructure construction and interface regulation on the OWS performance of TMSes was explored.In this paper,Hierarchical NiSe@MFe-LDH（M=Ni,Co,Mn,or Zn）heterostructure nanosheet arrays catalyst was constructed through hydrothermally hybridizing NiSe with Fe-based layered double hydroxide（LDH）.Benefiting from the unique sheet-on-sheet structure,rich heterogeneous interfaces,and strong electronic coupling and synergistic effect,the heterostructure effectively increases the specific surface area and active sites,regulates the electronic structure,optimizes the reaction adsorption energy,reduces the reaction energy barrier,and improves the energy conversion efficiency of OWS.Therefore,NiSe@MFe-LDH/NF heterostructure achieves excellent OER and HER performance.For OWS,it only requires potentials of 1.512 and 1.705 V to reach 10 and 100 m A·cm^-2respectively,which is superior over the precious metal catalyst Pt/C/NF||Ru O₂/NF（1.552 and1.722 V）,and it can work stably for at least 100 hours.