Research On Regulating Electronic Structure Of Molybdenum Disulfide And Their Electrochemical Hydrogen Evolution Performance

The widespread use of non-renewable energy such as natural gas,coal and oil lead to serious energy crisis and environmental pollution around the world.Hydrogen energy,as a clean energy,plays a crucial role in dealing with energy crisis and environmental pollution.Based on the problems of less active sites and poor conductivity of MoS₂,the electronic structure of MoS₂ is regulated by constructing nano-heterojunctions structures,modification of transition metal atoms,doping of anions,preparation defects,etc.Based on these aspects,a series of studies have been carried out,and the catalytic mechanisms of their excellentcatalytic performance improvement have been explored.The specific studies as follows:1.The spherical nano-heterostructure Ni₃S₄-MoS₂has been prepared by a one-pot hydrothermal method.It is showed that Ni₃S₄ is uniformly distributed on the MoS₂ nanosheets,and the morphology and structure of MoS₂ are maintained well,which is characterized by scanning electron microscope(SEM)and high-resolution transmission electronmicroscope(HRTEM).The construction of nano-heterostructure increases the conductivity of MoS₂ and activates the inert basal plane of MoS₂.X-ray photoelectron spectroscopy(XPS)and theoretical calculations show that the redistribution of electrons at the heterojunction interfaces leads to transfer some electrons from Ni with strong electronegativity to S,which is conducive to the adsorption of H^*by S atom,while partially oxidized Ni is beneficial to the adsorption of OH^*.Density functional theory(DFT)simulations indicate that the synergistic effect in the system with the chemisorption of H^*on the(002)plane of MoS₂ and OH^*on the(311)plane of Ni₃S₄ accelerate the rate-determining water dissociation steps of hydrogen evolution reaction(HER).The Ni₃S₄-MoS₂ exhibited a low overpotential of 116 mV at 10 mA cm^-2 in alkaline solution with corresponding Tafel slope of 81 mV dec^-1.Compared with pure MoS₂(235mV),the HER performance of this catalyst is improvedgreatly.2.Ni doped MoS₂ was etched with K₃[Co(CN)₆]to obtain Prussian blue analogue nanoparticles loaded on the surface of MoS₂ nanosheets with rich Mo vacancies.Then,NiCoP-MoS₂-V_Mo with excellent HER performance is obtained by phosphating chemical vapor deposition(CVD).SEM,HRTEM and inductively coupled plasma-optical emission spectrometry(ICP-OES)characterization showed that NiCoP nanoparticles are uniformly dispersed on the MoS₂ nanosheetswith rich Mo vacancies,which increases the active sites and conductivity of MoS₂.NiCoP nanoparticles are loaded on MoS₂ nanosheets,resulting in the transfer of NiCoP electrons to MoS₂,which contribute to the adsorption of H₂O by NiCoP nanoparticles.The increased electron density of S atoms in MoS₂ is conducive to the adsorption of H,thereby improving HER catalytic activity of NiCoP-MoS₂-V_Mo.DFT calculations show that the S atoms connected to Mo vacancies in NiCoP-MoS₂-V_Mo are hydrogen acceptors,and NiCoP nanoparticles are hydroxyl acceptors,which synergistically lower the intermediate energy barrier of the hydrolysis step and accelerate the HER reaction.The as-prepared catalyst exhibited a low overpotential of 87 mV with the corresponding Tafel slope of 90 mV dec^-1 as well as negligible current attenuation over 20 h.3.A dual monatomic Ru and Ni co-modified MoS₂is synthesized by wet chemical method.Due to the difference of electronegativity between different atoms,the highly electronegative Ni atoms anchor the single atoms Ru through the S atoms.Experiments combined with theoretical calculations indicated that the single Ru atoms were anchored through single Ni atoms with strong electronegativity,and most of the Ru atoms coordinated with the S were distributed on the Ni atop sites.This causes electrons to be transferred from Ru atoms to Ni atoms through S,resulting in the electric charge density of S atoms that bonded to Niatoms increases,while that of Ru reduces.DFT calculations demonstrate that the synergistic effect of the Ru/Ni-MoS₂ with S atoms bonded with Ni as hydrogen acceptor and single-atoms Ru as hydroxyl acceptor,effectively reduced the intermediate energy barrier of the water dissociation step.The as-fabricated Ru/Ni-MoS₂ exhibited a super-low overpotential of 32 mV at 10mA cm² with the corresponding Tafel slope of 41 mV dec^-1 as well as negligible current attenuation over 20 h,far surpassing that of Ru-MoS₂and Ni-MoS₂.4.After soaking MoS₂ in(NH₄)₂Ce(NO₃)₆,MoS₂ of O was obtained to replace part of S.The introduction of O atoms increases the active sites of MoS₂,improves conductivity,and induces the transition from 2H to 1T phase of MoS₂.DFT calculations reveal that the introduction of O atomswith strong electronegativity increases the electron cloud density of S atoms adjacent to O,optimizes the adsorption of H^*,and increases HER activity.The overpotential of as-fabricated O-MoS₂ at 10 mA cm^-2 is only120 mV in alkaline electrolyte,and long-term stability of over 20 h.