Design And Electrocatalytic Performance Of NiFe LDH Electrocatalyst Based On Core-Shell Structure

In order to achieve the strategic goal of carbon peaking and carbon neutrality,we should actively guide green technology innovation and vigorously develop new energy.As a renewable energy source,hydrogen energy has a wide range of sources,high energy density,and is green and pollution-free.It has great application prospects in energy storage,aerospace,military and other fields.Water electrolysis is an important means of hydrogen production,and high-purity hydrogen can be obtained.However,the high overpotential limits its use in large-scale hydrogen production.Oxygen evolution reaction（OER）is the rate-controlling step of the water electrolysis reaction,and its overpotential seriously affects the overall overpotential.By developing high-performance electrocatalysts to reduce the overpotential of the OER process,the hydrogen production efficiency can be effectively improved and energy waste can be avoided.Nickel-iron layered double-metal hydroxide（Ni Fe LDH）,with its low cost,wide sources,and tunable metal ratio,is considered to be a potential electrocatalyst,but it suffers from insufficient exposure of active sites and low intrinsic catalytic activity.Disadvantages limit its further application.In this paper,the active site of Ni Fe LDH is effectively exposed by synthesizing a catalyst with a core-shell structure,and the electronic structure of Ni Fe LDH is effectively tuned by constructing a p-n junction and cationic vacancies,which further improves the OER performance while retaining the core-shell structure.In addition,by combining Ni Fe LDH with Co Se,a bifunctional catalyst with a core-shell structure was constructed to realize the overall water splitting at low voltage.（1）The P-Co₃O₄@Ni Fe LDH core-shell structure catalyst was synthesized by hydrothermal method and electrodeposition method,which achieved a significant improvement in OER performance,and only 255 m V overpotential was required to reach a current density of 100 m A/cm².Through characterization analysis,it was found that the core-shell structure catalyst effectively exposed a large number of Ni Fe LDH active sites,and the open channels were conducive to the full contact between the active sites and the electrolyte solution.In addition,P-Co₃O₄ is a P-type semiconductor,and after contacting with n-type Ni Fe LDH,the strong electronic interaction optimizes the electronic structure,and the synergistic effect of the exposure of the active site and the electronic structure achieves excellent oxygen evolution activity.（2）Part of Fe was replaced by Cr and Ni Fe Cr LDH catalyst was synthesized by electrodeposition method,the Ni Fe Cr LDH-V_Cr rich in Cr cation vacancies was subsequently prepared by alkaline etching,electrochemical tests show its excellent OER performance,which can be attributed to the unsaturated active sites and changes in electronic structure.Further,Ni Fe Cr LDH was deposited on Co₃O₄ nanosheets by electrodeposition method,and after the same etching treatment,Co₃O₄@Ni Fe Cr LDH-V_Cr catalyst with core-shell structure was synthesized,Co₃O₄@Ni Fe Cr LDH-V_Cr retains the core-shell morphology and only forms a large number of cation vacancies on the surface of Ni Fe LDH.This providing multi-dimensional mass transfer channels and gas release pathways for the OER process,and exposes more unsaturated active sites.The formation of cation vacancies tunes the electronic structure of the surrounding metal ions,resulting in a significant improvement in OER performance.（3）Co Se@Ni Fe LDH core-shell bifunctional catalyst was constructed by loading Ni Fe LDH onto Co Se nanosheets by one-step electrodeposition.Benefiting from the hierarchical structure of the catalyst and the good HER performance and electrical conductivity of Co Se,the Co Se@Ni Fe LDH exhibits simultaneously improved OER and HER performance.Through electrochemical tests and XPS characterization,it is found that Co Se@Ni Fe LDH has a significantly improved electrochemically active surface area,and there is a strong electronic interaction between Co Se and Ni Fe LDH,which increases the valence state of Ni and Fe ions,which is conducive to the adsorption of OH^-and effectively reduces the OER overpotential.When used for overall water splitting,only a low voltage of 1.477 V is required to drive a current density of 10 m A/cm²,and it has a long-term working stability of 10 h.