Preparation Of Self-supporting Cobalt-based Oxides And Control Of Catalytic Performance For Water Electrolysis

The excessive consumption of fossil fuels has led to a serious reduction of traditional energy sources and the deterioration of the environment.The development of low-cost,highly active and durable renewable energy technologies,such as fuel cells and metal air cells,as well as some renewable processes,such as electrolytic water,is a scientific challenge facing the world today.Electrolytic water can be seen as two half reactions,namely cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）.Therefore,it is very attractive to design efficient,stable,durable and economical catalysts for water electrolysis.Among them,transition metal matrix composites represented by cobalt have been widely studied in the field of water electrolysis.At the same time,in recent years,carbon dot（CDs）has also been used in the field of electrocatalysis because of its advantages of regulating carrier morphology,promoting electron transfer and high specific surface area.In this paper,a series of novel cobalt-based metal composites were prepared for efficient water decomposition.The details are as follows.（1）In this chapter,cobalt-iron-based metal oxides were grown on foamed nickel in situ,and the morphology of the catalysts CoFeO_x@NCDs-y/NF（x=4/3,y=0,25,50,100 mg）was adjusted by changing the amount of nitrogen-containing carbon points,so as to explore the effect of carbon points on the performance of electrochemical water decomposition.After full characterization and performance test of the prepared materials,it was found that the fine mesh CoFeO_x@NCDs-50/NF showed the best OER and HER activity in 1 M KOH compared with other catalysts.When the current density was 10 mA·cm^-2,the overpotential was 114 mV and 153 mV,respectively.After 20 hours of electrochemical test,it was found that it had excellent stability.In addition,the catalyst also has excellent comprehensive water decomposition performance,and the battery voltage is 1.575 V at 10 mA·cm^-2.Due to the doping of appropriate amount of carbon points,the fine network structure formed by the catalyst increases the specific surface area,exposes more active sites,increases the contact area with the electrolyte,and promotes the diffusion of electrolyte and gas.at the same time,the strong coupling caused by nitrogen doping also affects the overall interfacial electron transfer,thus improving the catalytic activity.（2）In this chapter,we also synthesized a series of spinel MCo₂O₄（M=Ni,Mn,Cu,Co）nanomaterials on foamed nickel by simple hydrothermal method and calcination method,and characterized their structure and oxygen evolution properties.It is found that the other three materials NiCo₂O₄,Mn Co₂O₄ and Cu Co₂O₄ have better OER properties than Co₃O₄@NF.Among them,NiCo₂O₄@NF has the best performance,which only needs the overpotential of 154 mV to reach the current density of 10 mA·cm^-2.At the same time,NiCo₂O₄@NF also has the smallest Tafel slope and excellent stability.The high specific surface area of NiCo₂O₄@NF can provide larger active area and more contact sites with electrolyte in the electrocatalytic reaction,thus greatly improving the efficiency of charge transfer.At the same time,the substitution of metal atoms can adjust the electronic structure of the catalyst to a certain extent,promote ion diffusion,thus showing excellent catalytic performance.