Design,Construction And Electrocatalytic Properties Of Three-Dimensional Nickel-Iron Based Oxygen Evolution Electrode

Fossil fuels are the main energy in the world,and their reserves are limited.The burning of fossil fuels brings increasingly serious environmental pollution problems.Therefore,the development of clean renewable energy has attracted great attention of scientists.Amid renewable energy sources,hydrogen energy is an optimal green energy.Among numerous technologies of hydrogen production,electrolysis of water is a promising approach,which has many advantages,such as the abundant materials,simple process and high purity of product.However,the high energy comsumption is needed during the electrolysis of water.The high cost has severely hindered its extensive application.Moreover,multistep proton-coupled electron transfer and the generation of more than one intermediate during the oxygen evolution reaction（OER）make it to be a kinetically sluggish process.So,catalysts with high electrocatalytic activity,low overpotential,earth-abundant and long life are urgently needed.In this dissertation,the controlled sysnthesis of the nickel（-iron）based nanosheet precursor is realized,and then the three-dimensional porous nickel（-iron）selenide nanosheets oxygen evolution electrode is obtained through selenation of the precursor by a hydrothermal process.Meanwhile,the electrocatalytic performance of the three-dimensional oxygen evolution electrodes are tested,and the effect on electrocatalytic activity of selenation and Fe-incoporation are also studied.In addition,the nickel-iron based nanosheet,namely the nickel-iron layered double hydroxide has been in-situ grown on the substrate of reduced graphene oxide/nickel foam（rGO/Ni）.The catalytic activity of this electrode is also studied.The obtained results are as follows:（1）The controlled sysnthesis of nickel（-iron）selenide nanosheets and precursors are achieved.The uniform and ultrathin nickel（-iron）based nanosheet precursor is prepared through the mixed-solvent（water and ethylene glycol）thermal process and the optimization of NH₄F,the feed ratio of nickel,iron and solvent.Futhermore,the three-dimensional porous nickel（-iron）selenide nanosheets oxygen evolution electrode is realized by selenation of the precursor with a hydrothermal process.In addition,the morphology,phase and elemental content of the materials are characterized by different characterization methods.The composition of selenide nanosheets can be comfirmed as NiSe₂ and(Ni_0.75Fe_0.25)Se₂,respectively.（2）The electrocatalytic performance of oxygen evolution reaction based on three-dimensional porous nickel（-iron）selenide nanosheet electrode is realized.The porous(Ni_0.75Fe_0.25)Se₂ nanosheets electrode exhibits the highest catalytic acitivity with a small overpotential of 255 mV at a current density of 35 mA cm^-2,and a low Tafel slope of 47.2 mV dec^-1.The porous nanostructure formed by the selenation process brings larger contact area between oxygen electrode and electrolyte,and enhances electronic conductivity and promotes the release of oxygen bubbles from surface,and raises the catalytic activity of the electrode.（3）The three-dimensional NiFe-LDH nanosheets oxygen evolution electrode based on rGO/Ni substrate is realized through a mixed-solvent thermal process,and its performance is also obtained.The rGO/Ni substrate is prepared by a simple water bath method,and it can be used to support NiFe-LDH nanosheets.This electode displays excellent catalytic activity with a small overpotential of 249 mV at a current density of 35 mA cm^-2,and a low Tafel slope of 52.6 mV dec^-1.The rGO can be an effective electron transport network during the OER and also improves the catalytic reaction kinetics.Besides,the rGO improves the stability of the electrode by enhancing the bonding between nanosheets and substrate.