Study On The Electrocatalytic Performance Of Transition Metal Compounds/MXene Composites For Hydrogen Evolution Reaction

As a kind of clean energy,hydrogen energy has attracted much attention in the world.There are many ways to obtain hydrogen energy,among which electrolysis of water is an efficient and rapid method to produce hydrogen.Platinum（Pt）is the best catalyst for water electrolysis at present,but some non-precious metal catalysts are favored because of their low cost and abundant reserves.In this paper,a series of highly efficient carbon/transition metal multi-component electrocatalysts were designed and prepared with abundant and cheap two-dimensional MXene composites of transition metals nickel and cobalt hybrid as the research object.The microstructure and electrocatalytic hydrogen evolution（HER）activity and stability of the electrocatalysts were preliminarily studied,and the roles of each component in HER process were analyzed.The correlation between microstructure and properties of catalysts was established to provide experimental basis and theoretical support for the construction of high efficiency and low cost electrocatalysts using multi-component synergies.The specific research contents are as follows:1.Co-NCNT/MXene composites were prepared by simple high temperature annealing.Nitrogen-doped carbon nanotubes（NCNT）were grown vertically on MXene,and a three-dimensional interconnected charge transfer network was constructed.Carbon rich materials grow into NCNT by annealing at high temperature with transition metal as catalyst.By growing carbon nanotubes on the surface of MXene lamella,the vertically ordered array structure can enhance its electrical conductivity and provide more active sites for ion diffusion,thus improving the electrocatalytic activity.Co-N_x,cobalt metal and nitrogen-doped carbon nanotubes in Co-NCNT/MXene are active sites for hydrogen adsorption.This composite structure enables Co-NCNT/MXene to have remarkable HER properties,i.e.low HER overpotential,small Tafel slope,large electrochemically active surface area and good long-term stability.2.By a simple hydrothermal reaction process,Ni nanoparticles（Ni-NG/MXene）were supported in situ on N-doped graphene（NG）and MXene composite carbon support using MXene and GO as carbon support and Na BH₄ as reducing agent,and were used as an efficient electrocatalyst for HER in acidic and alkaline electrolytes.In the absence of the auxiliary catalyst containing precious metals,the overpotential is relatively low in 1 M KOH and 0.5 M H₂SO₄,that is,when the current density is 10 m A cm^-2,the overpotential is 168m V and 134 m V under acidic and alkaline conditions.And the smaller Tafel slopes are 76.63and 70.49 m V dec^-1,indicating that Ni-NG/MXene has good HER performance,which is due to the high electrochemically active surface area and the synergistic effect between well-dispersed Ni nanoparticles and three-dimensional porous NG/MXene.In addition,long-term stability tests show that Ni-NG/MXene composites have good electrocatalytic stability in both acidic and alkaline electrolytes.3.Co Ni₂S₄/MXene composite was prepared by in-situ growth of Co Ni₂S₄/MXene on MXene lamellar by hydrothermal reaction and high temperature annealing process.Co Ni₂S₄/MXene composite was used as an efficient electrocatalyst for HER in alkaline electrolyte.When the current density of Co Ni₂S₄/MXene was 10 m A cm^-2,the prepared Co Ni₂S₄/MXene showed a low overpotential of 159 m V and a small Tafel slope(71.04 m V dec^-1),showing good HER performance.This was attributed to the fact that the large specific surface area of MXene could inhibit the stacking of Co Ni₂S₄ and increase the number of active sites.The growth of Co Ni₂S₄ on the surface of MXene also inhibited the aggregation of MXene.In order to further improve HER performance,Ce doping was performed on the basis of Co Ni₂S₄/MXene,and samples with different Ce doping amounts were prepared for electrochemical characterization.The results showed that Ce doping significantly improved the performance of Co Ni₂S₄/MXene,which may be attributed to the exposure of abundant catalytic active sites and the optimization of the electronic structure of the catalyst with Ce coupling,thus reducing the catalytic energy barrier and enhancing HER activity of Ce-Co Ni₂S₄/MXene catalyst.