Controling Of Cation Vacancies In In-situ-NiFe-LDH As Highly Efficient Oxygen Evolution Electrocatalysts

Water electrolysis is a sustainable method for hydrogen production due to simple and green process.However,the oxygen evolution reaction?OER?is considered to be the main factor limiting the development of water electrolysis because of its slow kinetics and high overpotential.Recently,the layered double hydroxides?LDH?as an OER electrocatalyst has attracted much interest due to its tunable chemical composition and unique electronic structure.NiFe-LDH is recognized as a good OER electrocatalyst due to the synergetic effect of the tunable Ni²⁺and Fe³⁺.However,due to the limitation of NiFe-LDH's own structure and charge conductivity,the active sites of NiFe-LDH are not exposed sufficiently,and the catalytic activity of the active sites cannot be utilized to the maximum degree.The cation vacancy in NiFe-LDH is the most effective method to improve its mass transfer ability,increase its number of active sites,and improve its OER performance.However,the existing methods for preparing cation vacancies rich-NiFe-LDH has the disadvantages of complicated process,expensive equipment,high toxicity of raw materials,long preparation period and so on.And Variety preparation method needs to add a large amount of conductive agent and adhesive,reducing the OER catalytic activity and stability of the electrode.In this work,an anodic film with strong binding force was in-situ fabricated on the 1j83alloy.And then,the anodic film was used as precursor to obtain NiFe-LDH by hydrothermal treatment.During the hydrothermal treatment,cation vacancies were appeared because of the dissolving of Mo.This study also showed that the content of cation vacancies in NiFe-LDH can be controlled by changing the hydrothermal temperature.The research showed that the optimal parameters for anodization were as follows:1wt.%NH4F+80wt.%H3PO4 was used as the electrolyte composition,anodizing voltage of 5 V and anodizing time of 15 min.The optimal parameters of hydrothermal treatment were as follows:0.2 M NaOH aqueous solution was used as a hydrothermal solution and hydrothermally prepared at 120°C for 4 h.The electrochemical characterization of the cation vacancies rich-NiFe-LDH catalyst was carried out.The results showed that the OER performance of the NiFe-LDH electrode prepared in this work is very good and the overpotential is only 250 mV when the current density is 10 mA cm^-2,and the current density at the 300 mV overpotential reaches a staggering 104 mA cm^-2,which is greatly improved compared to the commercial IrO₂/C catalyst;the NiFe-LDH electrode prepared in this study can be directly used as anode material for water electrolysis without any adhesive.NiFe-LDH electrode prepared in this study also exhibited high stability with OER overpotential almost have no raise after 24 hours'water electrolysis at 10mA cm^-2.The preparation method of the cation vacancies rich-Ni Fe-LDH electrode in this study is expected to be extended to the research of other oxygen evolution electrodes and provide the key materials for the industrial application of hydrogen production by electrolysis of water.