Synthesis And Electrocatalytic Performance Of Molybdenum Disulfide

Splitting of water via electrolysis is broadly considered as one of the most prospective strategies for generating hydrogen,a clean and renewable source of energy.Noting that the water splitting performance is affected by both the oxygen evolution reaction(OER)at the anode and the hydrogen evolution reaction(HER)at the cathode,resulting in an excessively high working potential and limits the efficiency of energy conversion.Therefore,there is always a need for highly efficient electrocatalysts to improve reaction kinetics,reduce working potential,and reduce energy loss.The two-dimensional(2D)MoS₂ electrocatalyst has received great attention from researchers due to its unique physical properties and potential catalytic activity.However,the catalytic activity of MoS₂ is severely limited by its weaker conductivity and limited active sites.Therefore,in this paper,for these two problems,the control methods such as heteroatom doping,in-situ electrochemical oxidation tuning and compounding have been optimized and modified in order to obtain high-performance electrocatalytic materials.The specific studies are summarized as follows:(1)N doped MoS₂(N-MoS₂),P doped MoS₂(P-MoS₂)and As doped MoS₂(As-MoS₂)were prepared by a simple one-step hydrothermal method.Characterization analysis shows that N,P and As were successfully doped into MoS₂,and the morphology and crystal structure did not change significantly.Among them,As-MoS₂ nanosheets exhibit excellent catalytic performance for HER,with a small overpotential of 200 m V at a current density of 10 m A cm^-2.Moreover,the As-MoS₂ catalyst has excellent long-term stability.In addition,the electrochemical oxidation of the edge leads to a significant suppression of the catalytic performance of the original MoS₂,while the catalytic performance of the As-doped MoS₂ nanosheets is less affected by the edge oxidation,which indicates that the base surface has catalytic activity.DFT calculations showed that the calculated value of?G_H*of As atoms is only-0.07 e V,indicating that it has excellent catalytic hydrogen evolution performance.In addition,the p-orbital centers below and near the Fermi level play an important role in the H adsorption process,and the closer?p is to the Fermi level,the weaker the H-nonmetal atom bond.Proper?_p can ensure proper bond strength with H,and further affect the catalytic activity of HER.(2)The N and F co-doped MoS₂(NF-MoS₂)nanosheets were prepared by a simple one-step hydrothermal method.The characterization analysis shows that N and F were successfully doped into molybdenum disulfide,and the morphology and crystal structure did not change significantly.Due to the synergy of chemical co-doping,the prepared NF-MoS₂ catalyst exhibits excellent catalytic hydrogen evolution activity,with a low initial overpotential of 110 m V,a small Tafel slope of 57 m V dec^-1 and excellent long-term stability.DFT calculations show that F atoms induce the activation of N atoms on the base surface.In other words,the N on the NF-MoS₂ base surface can serve as a new active and adjustable catalytic site.The inert base surface of MoS₂ can be activated by the synergistic effect of N and F co-doping,and the catalytic active sites increase,which leads to the greatly improved catalytic activity of MoS₂.In addition,the co-doping of F and N in the MoS₂ nanosheets can also lead to higher intrinsic conductivity.(3)A unique Mo Ox@N-doped MoS_2-x catalyst was synthesized by in-situ electrochemical oxidation adjustment of N-doped MoS₂.Characterization analysis shows that after electrochemical oxidation adjustment,the crystal structure is poor,there are many defects in the crystal and the valence of Mo is relatively high.Since an appropriate amount of oxygen evolution active site Mo Ox is formed on the surface of N-MoS₂,its oxygen evolution performance is optimized.The internal N-MoS₂ acts as a conductive carrier to ensure fast charge transfer.Among them,Mo Ox@N3-doped MoS_2-x shows excellent catalytic oxygen evolution performance,with a very low overpotential of 270m V at 10 m A cm^-2,a small Tafel slope of 61 m Vdec^-1 and satisfactory stability.DFT calculations show that internal N atom doping can enhance electronic conductivity.The formation of external Mo Ox increases the electrophilicity of the adsorbed O*species,and therefore promotes the formation of adsorbed OOH*intermediates through nucleophilic attack,thereby accelerating the deprotonation of OOH*through the electron withdrawing induction effect to generate O₂.(4)The active site Ni Fe nanosheets were loaded onto 2D MoS₂ by in-situ reduction of the metal precursors,and Ni Fe/MoS₂ composites were prepared.In this way,not only can the aggregation of Ni Fe nanosheets be suppressed,but also they can be uniformly exposed to the inert substrate plane of the 2D MoS₂.At the same time,the synergy between the gas generated during the in-situ reduction of the metal precursor and the ultrasound facilitates the exfoliation of MoS₂,thus helping to form a thin-layer-layer structure.The characterization analysis shows that the thickness of the Ni Fe/MoS₂ composite material is about 7 nm,and it shows strong interface coupling and electron transfer.Due to the layer-to-layer interaction,Ni Fe/MoS₂ exhibits excellent catalytic oxygen evolution performance,with a very low overpotential of 260 m V at 10 m A cm^-2,a small Tafel slope of 48 m Vdec^-1 and satisfactory stability.DFT calculations show that there is an interaction between layers and there is electron transfer,which regulates the electronic structure of the active site Ni Fe,affects the adsorption energy of the intermediate during the oxygen evolution process,and thus affects the oxygen evolution activity of the active site.