Preparation Of Oxides Of Iron,cobalt And Nickel And Their Performances For Electrocatalytic Water Splitting

With the reduction of fossil fuels and the increasing problem of environmental pollution,the future development of society will have to rely on sustainable renewable energy.Hydrogen has the characteristics of high calorific value,zero carbon emissions,easy transportation and abundant resources,and the only product after hydrogen combustion is water that does not pollute the environment,so hydrogen energy is recognized as a new energy source to replace traditional fossil fuels.The temperature required for the thermal water splitting to produce hydrogen is extremely high and difficult to achieve.The electrocatalytic water splitting can be carried out at room temperature,so electrocatalytic water splitting is considered a promising method for large-scale hydrogen production.The electrocatalytic water splitting consists of two half reactions,hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.The major challenge to complete the electrocatalytic water splitting is to overcome the reaction sluggish kinetics in these two half reactions.In particular,the OER reaction,which involves the transfer of four electrons,is an intrinsic sluggish kinetics process with a large overpotential.In order to efficiently realize the electrocatalytic water splitting to produce hydrogen,it is important to find a high-efficiency electrocatalyst that can reduce the overpotential in the HER and OER reactions.To date,in alkaline solutions,Pt-based catalysts are the most effective active materials for HER,RuO₂ and IrO₂ are the best electrocatalysts for OER.However,due to the scarcity and high price of these precious metal catalysts,their practical application in the electrocatalytic water splitting to produce hydrogen is limited.Therefore,it is very important to develop catalysts that with abundant content in the earth's crust,low price,high selectivity,low overpotential and good stability.Transition metal oxides have attracted great interest from researchers because of their wide source,low price and excellent catalytic performance.Now they are widely used for energy conversion and storage.At the same time,transition metal oxides are considered to be the most promising electrocatalyst.In this paper,oxides of transition metals,iron,cobalt and nickel were designed and synthesized by a simple method,and the performances of hydrogen evolution,oxygen evolution and overall water splitting of these materials were studied by electrochemical methods.The main contents of this article are as follows:1.NiCo₂O₄ was synthesized by adding different amounts of graphene oxide?GO?with a simple hydrothermal method and calcination process,and it was coated on a stainless steel mesh?SS mesh?to study the performance of HER and OER.The measurement results of HER and OER in alkaline solution showed that the NiCo₂O₄catalyst was synthesized with different GO amounts has different HER and OER activities.NiCo₂O₄ on SS mesh?NiCo₂O₄-10@SS mesh?has the highest activity of HER and OER when the GO amounts is 10 mg.In the HER,it generates an overpotential of 0.205 V at a current density of 10 mA cm^-2.In the OER,a current density of 10 m A cm^-2 is generated at an overpotential of 0.263 V.In addition,whether in HER or OER,NiCo₂O₄-10@SS mesh shows good stability.2.Several commonly used conductive carriers have been studied under alkaline conditions.Nickel foam exhibits excellent HER performance,with an overpotential of0.217 V at a current density of 10 mA cm^-2,and a Tafel slope of 130 mV dec^-1.The stainless steel mesh shows excellent OER performance.The overpotential is 0.277 V at a current density of 10 mA cm^-2,and the Tafel slope is 51 mV dec^-1.At the same time,both nickel foam and stainless steel mesh showed high stability during the HER and the OER,respectively.In addition,in a two-electrode system with nickel foam as the cathode and stainless steel mesh as the anode,the voltage required is 1.74 V when the current density reaches 10 mA cm^-2.3.Spinel-type ternary transition metal oxides of iron,nickel and cobalt with a composition of Fe_xNi_1-xCo₂O₄?x=0,0.05,0.1,0.15,0.2?were synthesized by a simple hydrothermal method and calcination,and it was coated on a nickel mesh?Ni mesh?.Under basic conditions,the measurement of the OER shows that Fe_0.1Ni_0.9Co₂O₄@Ni mesh has the best OER performance among these prepared catalysts,with an overpotential as low as 271 mV at 10 mA cm^-22 of current density,the Tafel slope is 48mV dec^-1,which is superior to RuO₂ and most reported non-precious mixed metal oxides electrocatalyst.In addition,Fe_0.1Ni_0.9Co₂O₄@Ni mesh also exhibits excellent stability during long-term electrolysis in alkaline solution.