Multi-strategy Control Of The Electronic Structure Of MoS₂ And Its Electrocatalytic Hydrogen Evolution Performance

With the fourth industrial revolution,the global transition to new energy has begun.Hydrogen energy as an energy released during the chemical change of hydrogen is an important energy type with secondary energy properties.Hydrogen produced by electrolyzed water is very pure,without any impurities,without secondary purification and with a small construction locality.It is a promising commercial hydrogen production method.However,at present,the energy consumption of hydrogen production by electrolyzed water is high.Although the precious metal catalysts Pt/C?RuO₂?and IrO₂ have good catalytic performance and can reduce their energy consumption,their cost is high,and they are not suitable for large-scale applications.Inorganic non-precious metal semiconductor two-dimensional material MoS₂ has lower hydrogen Gibbs adsorption free energy,and its performance in electrocatalytic hydrogen evolution reaction can be comparable to that of precious metal Pt.However,MoS₂ with a semiconducting phase structure also has large impedance and poor conductivity,which is not conducive to electron transfer in electrocatalytic reactions,and has few catalytic active sites,which makes its catalytic activity not ideal enough for practical application.Therefore,how to improve the hydrogen production activity of MoS₂ so that it can truly replace the precious metal catalyst has become the focus and problem of research in recent years.This work attempts to explore two completely different modification strategies to improve the electrocatalytic hydrogen evolution activity of MoS₂:on the one hand,constract Cu mesh@Cu NW@MoS₂ three-dimensional self-supporting structure;on the other hand,use the defects and piezoelectric properties of MoS₂ Piezoelectric electrons are generated by simple liquid phase ultrasound and stirring,so that Pd²⁺in a high valence state is reduced to prepare small-sized Pd-doped MoS₂,thereby increasing the active site of MoS₂,improving its conductivity,and solving its powder-like difficulty in solid support Practical application issues such as Our work mainly starts from the following three parts:?1?Preparation of three-dimensional self-supporting Cu mesh@Cu NW@MoS₂ electrode and its electrocatalytic hydrogen evolution performanceUsing copper mesh with high purity and good conductivity as the substrate,Cu?OH?₂ Nanowire?Cu?OH?₂ NW?is grown in situ on the surface by alkaline etching and initiator induction,and then further in a hydrogen argon atmosphere By fine-tuning the firing temperature and time,the Cu?OH?₂ NW on the surface is reduced to Cu Nanowire?Cu NW?in one step to build a Cu mesh@Cu NW three-dimensional self-supporting electrode substrate,and finally using DMF as a solvent through solvothermal method Pyrolysis of ammonium tetrathiomolybdate,in-situ growth of ultra-thin molybdenum disulfide on copper nanowires supported on copper mesh.SEM and XRD proved that we successfully prepared this Cu@Cu NW@MoS₂ three-dimensional self-supporting electrocatalyst.Through linear voltammetry?LSV?testing,we found that Cu@Cu NW@MoS₂ exhibited a super High current-carrying efficiency,the limit current is as high as 320 mA at the limit voltage of-480 mV?vs RHE?,and the initial hydrogen evolution potential is about-200 mV?vs RHE?.The two-dimensional ultra-thin structure of MoS₂ supported by copper nanowires makes it easier to expose the active sites,which is an important reason for improving the catalytic activity of MoS₂.This method also has the potential to achieve large-scale preparation.?2?Preparation of single-site Pd-modified MoS_2-B by in-situ redox method and its electrocatalytic hydrogen evolution performancePdCl₂ was selected as the source of palladium,MoS_2-B with S defects was used as the substrate,and MoS_2-B with single-site Pd modification was prepared by in-situ oxidation-reduction method using molybdenum disulfide surface defect sites.The effects of Pd source,theoretical doping amount of Pd and reaction temperature on catalyst structure and electrocatalytic hydrogen evolution activity were investigated.The results show that there are no metallic Pd nanoparticles on the surface of MoS_2-B,and Pd in Pd-MoS_2-B exists in divalent form.Compared with pure MoS_2-B,the binding energy of Mo and S in Pd-MoS_2-B has changed significantly.There is a certain bond between Pd and MoS_2-B,so that Pd²⁺is embedded in the lattice of MoS_2-B to replace The location of the original Mo³⁺.Linear voltammetry?LSV?results show that the initial hydrogen evolution potential of Pd_3%-MoS_2-B is reduced to-92 mV,which is200 mV lower than that of undoped MoS_2-B,Tafel slope reduced from 115mV/dec to50mV/dec,indicating that the modification of Pd at a single point can make MoS_2-B-B electrocatalytic performance has been significantly improved,which may be modified with the unit point Pd to change the surface electronic state of MoS_2-B,which is more conducive to reducing the adsorption energy of H atoms on the catalyst surface.This work also attempts a new exploration approach for the preparation of small-sized catalysts.?3?The effect of different MoS_2-B substrates on the performance of Pd/MoS_2-BFirst,the effects of different temperatures on the structure and properties of MoS_2-B substrate were studied.XRD results show that as the calcination temperature increases,the crystallinity of MoS_2-B increases and the number of defect sites decreases.At the same time,the semiconductor characteristics are more significant,and the conductivity becomes worse.Linear voltammetry?LSV?polarization curve test results found that as the calcination temperature increased,the electrocatalytic hydrogen evolution performance of MoS_2-B decreased or even deactivated.It shows that the reduction of MoS₂ defect sites and the increase of crystallinity after roasting are not conducive to electrocatalytic hydrogen evolution reaction.The inactivation of MoS_2-B obviously cannot further modify Pd ion.At the same time,we adjusted the preparation solvent from pure water to a mixed solvent of water and ethanol,and explored the effect of the addition of ethanol on Pd modified MoS₂.The electrocatalytic hydrogen evolution activity showed that ethanol solvent had no significant effect on the preparation of the catalyst.We have also applied this method to other structures of MoS_2-B.The study found that:using the same method for Pd doping on defective MoS₂-3D,the decorated Pd-MoS₂-3D electrocatalytic hydrogen evolution activity was significantly improved It shows that this method can be used to prepare MoS₂ materials modified by Pd at a single point due to its certain universality.