Study On Catalytic Performance Of Three-Dimensional Conductive Sulfide Composite/derivative Materials

Hydrogen is considered to be a carrier of high-calorie,zero-carbon clean energy and has shown broad application prospects in meeting industrial and social needs.However,the high cost and scarcity of precious metal-based catalysts used in electrocatalytic hydrogen production technology have limited their widespread use and production.Therefore,it is imperative to develop non-precious metal catalytic materials with high activity and high stability.The??type edge structure of the transition metal MoS2 is similar to the active site in the nitrogenase.Theoretical calculations show that the adsorption hydrogen free energy of MoS2 edge structure is similar to that of Pt and exhibits a high catalytic activity,but its base structure is an inert area.At the same time,the electron mobility between the vertical MoS2 faces is lower than the electron mobility in the base surface,the resistance loss is increased by about three orders of magnitude.So that the catalytic efficiency of the bulk MoS2 is greatly reduced by the limitation of the edge active sites and the poor conductivity.Therefore,we need to develop conductive metal sulfides that expose high density active sites.In this paper,we use conductive transition metal sulfide as the main research object.We optimize the microstructure,parameters,structure and morphology of the target conductive sulfide to increase the number of active sites,increase the activity of active sites or enhance the stability of active sites.The full-water splitting catalytic performance of conductive metal sulfides was systematically studied,and the intrinsic relationship between surfacea/interface structure modification and catalytic performance was discussed.The main research contents of this thesis include the following aspects:1.Based on the study of Ni3S2 materials,we have realized that Ni3S2 is a metal sulfide with good conductivity,which has a three-dimensional metal Ni-Ni bond structure unit.We further utilize the structure guiding effect of triblock copolymer P123 to construct a hollow Ni3S2 nanosphere electrocatalyst,which is composed of ultrathin nanosheets on the nickel foam substrate.Through effective nanostructure design,the obtained material exposes a large number of catalytic active sites,increases the contact area between the catalyst and the reactant,accelerates the mass transfer process,and improves the electrocatalytic activity.The materials give an impressive water-splitting current density of 10 mA cm^-2 at?1.45 V with remarkable durability for>100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer.This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal-based Pt/C and IrOx/C catalytic couple-the benchmark catalysts for HER and OER,respectively.2.We further prepared an ultra-small NixCo3-xS4 nanoparticle-modified Ni3S2nanosheet array by divalent Co cation exchange.A good catalyst should have moderate free hydrogen adsorption energy.The strategy effectively regulates the free energy of the adsorbed intermediate.The experimental results show that there is a large proportion of heterojunction interface between Ni3S2 and NixCo3-x S4 nanodomains,and its activity is higher than NixCo3-xS4/NF and Ni3S2/NF.Further DFT calculation results show that the adsorption hydrogen free energy of the S site at the interface of Ni3S2 and Co3S4 is 0.167eV,which is much smaller than that of single-phase Ni3S2 and Co3S4,indicating that NixCo3-xS4/Ni3S2/NF has some more efficient catalytically active sites at the interface.The activity of this electrolyzer,which contains NixCo3-xS4/Ni3S2/NF as electrocatalyst at both electrodes,is ca.7.6 times higher than that of the corresponding one containing Ni3S2/NF.The results presented herein could help paving the way towards the development of high-efficiency water splitting electrochemical devices.3.Based on the knowledge of the characteristics of conductive sulfides,we have also discovered a new conductive sulfide by screening and searching.In nature,FeS has two crystal structures,tetragonal and hexagonal.The hexagonal FeS is a kind of abundant internal mineral material and is a typical semiconductor.The tetragonal FeS material is a metastable phase conductive sulfide,which has the characteristics of intra-layer metal conduction and interlayer ion conduction,and is a good conductive sulfide.We first designed and synthesized FeS nanosheets,and then embedded the Fe@FeOxSy nanoparticles directly on the conductive FeS nanosheets by in situ electrochemical induction.Fe@FeOxSy demonstrates high catalytic performance with an industrial-grade high current density of 1000 mA cm^-22 at an overpotential of 366 mV.