Preparation And Electrochemical Performance Of Transition Metal Oxygen Evolution Catalysts

At present,fossil fuel is the main energy source for the development of society.However,the resources of fossil fuels are limited,and they will cause serious environmental pollution during the process.It is urgent to develop a renewable,clean and sustainable energy.Hydrogen as a new energy source has attracted extensive attention from researchers.Electrochemical water splitting is considered as the most efficient way to produce hydrogen.The electrolysis of water is generally divided into two reactions:the anodic oxygen evolution reaction（OER）and the cathodic hydrogen evolution reaction（HER）.However,the kinetic process of HER and OER is slow,it is highly necessary to develop an efficient and durable catalyst with excellent electrical conductivity to facilitate the reaction process.In this regard,precious metal based catalysts,such as ruthenium dioxide（Ru O₂）and iridium oxide（Ir O₂）have aroused widespread attention due to their high catalytic activity,but they are difficult to be widely used in industrial production due to their limited resources and high price.Therefore,it is very necessary to develop high efficient catalysts which are rich in earth resources.On the basis of the requirement of activity,stability and cost in industry,the transition metal oxides and sulfide materials are gradually favored.However,the inherent defects of single electrode materials limit their OER performance.In order to enhance their electrochemical activity,a series of improvement measures are taken in this paper,the main researches are as follows:（1）The self-supported Fe-doped Ni₃S₂nanosheets array（Fe-Ni₃S₂/NF）grown on Ni foam was synthesized by a two-step hydrothermal method.Fe-Ni₃S₂/NF has a unique nanosheet array structure,and shows superior electrocatalytic property with low overpotentials of only 287 m V to afford geometrical catalytic current densities of100 m A cm^-2in 1.0 M KOH.The main reason is that Fe doping increases the active surface area of Ni₃S₂and enhances the adsorption capacity of Ni₃S₂to water.In addition,Fe-Ni₃S₂/NF also demonstrates strongly long-term electrochemical stability,it can remain active for 25 hours in alkaline environment.（2）The self-supported core-shell nanostructure（Ni Co₂O₄@Co Fe-LDH/NF）consisting of Ni Co₂O₄nanowires and Co Fe double-layered hydroxide nanosheets grew on nickel foam was synthesized by hydrothermal method and calcination.Ni Co₂O₄@Co Fe-LDH/NF has a unique hierarchy and superior electrochemical oxygen evolution activity,it requires only 309 m V overpotential to reach the current density of 100 m A cm^-2in 1.0 M KOH,which is 32 m V less than pure Co Fe double-layered hydroxide nanosheets and 131 m V less than pure Ni Co₂O₄nanowires,respectively.It can maintain its catalytic stability and performance for 20 hours at 100m A cm^-2.（3）The self-supported core-shell nanostructure（Ni Co₂O₄@Ni Fe LDH/NF）consisting of Ni Co₂O₄nanosheets and Ni Fe double-layered hydroxide nanosheets grew on nickel foam was synthesized by hydrothermal and electrodeposition method.The special core-shell structure produces good interfacial synergistic effect and accelerates electron transfer.As an efficient oxygen evolution catalyst,the Ni Co₂O₄@Ni Fe LDH/NF only needs an overpotentials of 320 m V to achieve 100 m A cm^-2in 1.0 M KOH.In addition,the current density almost unchanged after 20 hours of electrochemical testing.