Study On The Preparation And Electrocatalysis Of Transition Metal Hydroxides And Their Derivatives

Hydrogen energy has high energy density,high calorific value and high combustion efficiency,so it is considered as a clean energy alternative to fossil fuels in the future.At present,hydrogen production by electrolysis of water is the most effective technology for high-purity hydrogen.In electrolytic water,the hydrogen evolution reaction（HER）of cathode and the oxygen evolution reaction（OER）of anode are critical to the overall hydrogen production efficiency.At present,platinum based and other precious metal catalysts are the most effective benchmark electrocatalysts,but their high price and low reserves limit their large-scale application in industry.Therefore,the development of low cost and high activity non noble metal catalysts to improve hydrogen production efficiency and reduce costs will play a key role in the development and utilization of hydrogen energy.Based on the development of high catalytic activity and low cost catalyst for electrolysis of water,this paper studies the modification of transition metal layered hydroxides.P-M LDH,a derivative of transition metal hydroxides,is prepared by doping to improve the catalytic performance of electrolysis of water;Transition metal oxides were prepared by calcination,and the catalytic performance of OER was improved by magnetic field.The research contents of this paper are as follows:（1）A new preparation method of P doped LDH nano sheets was proposed to prepare P-NiCoLDH,P-NiFeLDH electrocatalysts.First,Ni-P alloy layer was chemically deposited on foam nickel,and then P in Ni-P alloy layer was diffused into LDH by hydrothermal method to prepare P-M LDH nano sheet catalyst.P-LDH catalysts with different P content were prepared by changing the deposition time to control the amount of P doping,and their composition,structure,morphology and electrocatalytic performance were analyzed.The experimental results show that the current density of the P-NiCoLDH catalyst prepared by chemical deposition for 30 min can reach 30 mA cm^-2 only with 390 mV overpotential,its Tafel slope is 58.3 mV dec^-1,and the kinetic reaction rate is fast;The P-NiFeLDH catalyst prepared by 60 min chemical deposition has good electrocatalytic performance for both HER and OER.It only requires 115 and 210 mV over-voltage to provide a current density of 10 mA cm^-2.When it is used as anode and cathode for water electrolysis,the battery voltage at 10mA cm^-2 is 1.69 V,and it shows excellent stability for overall water decomposition within 15 h.（2）Three metal oxides（NiCo₂O₄,CoFe₂O₄,NiFe₂O₄）were prepared by calcination method,and their electrocatalytic activity for OER was investigated.The experimental results show that compared with commercial iridium oxide,the metal oxide has the following OER catalytic activity:NiFe₂O₄>IrO₂=NiCo₂O₄>CoFe₂O₄.The best OER catalytic activity is NiFe₂O₄.Its overpotential at 50mA cm^-2 is 420 mV,which is 40 mV less than commercial IrO₂.（3）The magnetic field assisted strategy was used to adjust and improve the catalytic performance of transition metal hydroxides for OER reaction.When three oxides were put into magnetic field for magnetization,NiFe₂O₄ was significantly improved.After being magnetized at 1T for 10 h,the NiFe₂O₄ electrocatalyst shows twice the current density of the original NFO at 1.664 V potential.OER activity is enhanced by the manipulation of Ni²⁺cation from theO_h site to the more active T_d site by applying magnetic field.