The Preparation And Electrocatalytic Performance Of Transition Metal Boron Compounds

Due to the energy crisis,the preparation of green,cheap,and renewable energy has become the primary goal of scientific researchers.Hydrogen energy is an ideal clean energy,among which electrocatalytic water splitting is an important method for producing high-purity hydrogen at room temperature.The hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）play a vital role in various electrochemical energy conversion devices,but the OER half reaction is a four-electron reaction process,which leads to its slow kinetics.As a result,the kinetic process of the entire electrolysis water is slow,which restricts the large-scale development of the hydrogen production industry by electrolysis.Therefore,the development of an economical and highly active electrocatalyst with excellent durability,high efficiency,and cheap OER is still the key to solving the problem.Recent studies have found that transition metal borides have better OER performance and are a new type of potential electrocatalyst,but they are prone to agglomeration during the preparation process.This thesis uses foamed nickel（NF）as the matrix and cobalt iron hydrotalcite（LDH:layered double hydroxide）as the branch.The low-temperature liquid deposition method is used to grow transition metal borides on the surface of the 3D three-dimensional iron-cobalt hydrotalcite.It solves the agglomeration problem of metal borides,increases the electrochemically active specific surface area of the material,and further improves the OER performance.The main research results are as follows:（1）The amorphous cobalt-iron-boron material was prepared on the foamed nickel substrate.In 1 mol·L^-1 KOH,Fe_0.3Co_0.7B_x/NF electrode material showed excellent catalytic performance of OER,at the current density of 10 m A·cm^-2,the oxygen evolution overpotential was 266 m V,and at the current density of 100m A·cm^-2,the oxygen evolution overpotential was only 337 m V,being lower than most previously reported transition metal boride electrocatalysts.In order to explore its activity in the HER reaction,it was found that the Fe_0.3Co_0.7B_x/NF electrode material also had good HER catalytic performance.In 1 M KOH,at the current density of 10m A·cm^-2,the hydrogen evolution overpotential was 225 m V.The experimental results show that the synergy between Fe-Co will greatly enhance the OER and HER catalytic activity of the material.（2）In order to reduce the agglomeration effect of transition metal borides,prepare by simple hydrothermal method different ratios of Fe Ni LDH and Fe Co LDH are intended to be used as boride growth support,and their OER catalytic performance has been studied.The study found that Fe_0.5Co_0.5 LDH/NF had the best OER catalytic performance.In 1 mol·L^-1 KOH,at the current density of 100 m A·cm^-2,the oxygen evolution overpotential required 365 m V,at the current density of 50m A·cm^-2after 10 hours of OER reaction,the overpotential remained basically unchanged from the initial value.（3）Innovatively use Fe_0.5Co_0.5 LDH/NF（FC LDH/NF）with a three-dimensional structure as the skeleton,and self-growth Fe_0.3Co_0.7B_x（FCB）on its surface to obtain FC LDH@FCB with better catalytic performance/NF.In 1 mol·L^-1 KOH,FC LDH@FCB/NF has excellent OER performance.At the current density of 100m A·cm^-2,the oxygen evolution overpotential was only 301 m V.And after 10 hours of OER reaction under 50 m A·cm^-2,the overpotential remained basically unchanged.At the same time,the catalytic activity in the HER reaction was studied,and the results showed that the Fe_0.5Co_0.5 LDH was used as the matrix,and the composite Fe_0.3Co_0.7B_x could improve the HER catalytic activity.When the current density was10 m A·cm^-2,hydrogen evolution overpotential was 197 m V.After 10 hours of reaction,the HER catalytic activity increased to 118.9%of the initial overpotential,which proved good HER catalytic activity and stability of FC LDH@FCB/NF.Being used as a catalyst for complete water dissolution,the terminal voltage was only 1.76V at current density of 20 m A·cm^-2.