Preparation And Performance Of Ni,Pd-doped MoS₂ Catalytic Material For Acidic Electrolyzed Water Towards Hydrogen Evolution

Hydrogen is a renewable and clean energy with high calorific value.Electrochemical water splitting offers the hope for sustainable hydrogen production.There is a high energy barrier in hydrogen evolution reaction（HER）of electrolyzed water,and the energy conversion efficiency is low.As a noble metal catalyst,Pt can effectively decrease the energy barrier,and it is commonly used as HER catalyst at present.But Pt is expensive and scarce,which greatly hinders their commercial application and restricts the development of water electrolysis technology.Two-dimensional layered MoS₂nanosheets are inexpensive,nontoxic and rich catalytic materials,and their edge sites have HER activity similar to Pt.However,due to the inert base plane and poor electrical conductivity of layered MoS₂,the actual HER activity of which is not high.Researchers have attempted to modify layered MoS₂through elemental doping engineering,phase transformation engineering and defect engineering in order to improve its HER catalytic activity.Among them,the doping of metal elements can activate the inert basal planes of MoS₂,which is one of the effective strategies to solve the conductivity,intrinsic activity,catalytic site density and stability of MoS₂simultaneously.In view of the hydrogen evolution reaction under acidic conditions,based on the high gravity technology,the morphology and structure of layered MoS₂are optimized by the metal doping engineering in order to synthesiz doped-MoS₂electrocatalytic material with high activity and stability for hydrogen evolution of electrolyzed water in this paper.The main research contents and results are summarized as follows:Pd-MoS₂catalyst was prepared by the spontaneous interfacial redox reaction and high gravity in-situ doping technique when Palladium acetate was used as Pd source and MoS₂nanosheets prepared by hydrothermal method was used as support.The effects of preparation process conditions on catalytic hydrogen evolution activity of Pd-MoS₂were studied,and the appropriate preparation conditions were determined as follows:the precursor solvent was acetic acid solution,Pd doping content was 7.3 wt%,high gravity level was 506 and reaction time was 2 h.Compared to pristine MoS₂,Pd dopant enlarges the interlayer spacing of MoS₂nanosheets,transforms part of the 2H phase into 1T phase,introduces the S vacancies and makes the S sitesadjacent to Pd（Pd-S*）become active sites.There is no obvious Pd aggregation on the surface of MoS₂nanosheets,and Pd is doped in MoS₂in the form of Pd（II）.The HER activity and stability of Pd-MoS₂are also significantly improved compared with pure MoS₂.The overpotential at 10m A cm^-2decreased from 265 m V to 96 m V,the Tafel slope decreased from112 m V/dec to 70 m V/dec,and the overpotential at 10 m A cm^-2increased by6 m V after 10000 CV cycle tests.In addition,compared to the traditional kettle stirring method,the reaction time of the high gravity method is short,the prepared Pd-MoS₂nanosheets have more 1T phase structures.Using nickel chloride as Ni source,Ni Pd-MoS₂catalyst was prepared based on Pd-MoS₂nanosheets through the hydrothermal reaction method.The appropriate preparation process conditions were studied and determined as follows:Ni doping content was 2.5 wt%,the doping sequence is Pd doping first and Ni doping later,hydrothermal temperature was 200℃and hydrothermal time was 12 h.The morphology and structural characterizations show that nickel is doped in MoS₂in the form of Ni（II）,and it further improves the conductivity of Pd-MoS₂.The doping of Ni activates the adjacent S sites to become the catalytic active sites.At the same time,the synergistic effect of Ni and Pd doping appropriately adjusts the electronic structure of MoS₂,so that it has the suitable hydrogen adsorption free energy,which improves the catalytic activity.Compared to Ni-MoS₂and Pd-MoS₂materials,Ni Pd-MoS₂exhibits an overpotential of 80 m V at 10m A cm^-2and Tafel slope of 62 m V/dec,which shows better electrocatalytic activity of hydrogen evolution.