| Energy security is a strategic issue related to the socio-economic development of a country.Currently,majority of the world's energy consumption comes mainly from fossil resources such as coal and petroleum.However,fossil resources are non-renewable and limited.In the case of fossil resources,inevitable environmentally harmful substances such as soot,carbon dioxide,nitrogen oxides,and sulfides are generated.Therefore,in the process of using fossil energy,the countries also face the threats that affect environmental security.With the increasing tension of fossil energy and the growing awareness of environmental safety issues,it is particularly important to develop new,efficient,clean and sustainable energy sources.The zinc-air battery shows a high energy density,and oxygen is used as a reactant at the positive electrode and stored outside the battery until it is discharged,so research on zinc-air batteries has attracted attention.Recently,iridium oxide and ruthenium oxide have been found to have excellent oxygen evolution reaction(OER)catalytic properties,and platinum and platinum-based catalysts exhibit excellent catalytic activity in oxygen reduction reaction(ORR),but their reserves are less,and they are rare.Also,it is expensive,and its high price greatly limits their practical application.Therefore,it is necessary to explore new cheap,efficient and stable materials to replace precious metal catalysts.Through researchers' work,it has been found that metal oxide catalysts exhibit excellent electrocatalytic properties,such as catalysts formed by metals such as iron,nickel,and cobalt.In addition,the self-supported electrode exhibits superior electrocatalytic performance and practicability,compared to a catalyst using a binder,due to its good electrical conductivity and flexibility.In this thesis,after simple electrodeposition and air annealing processes nickel-cobalt oxide nanosheets were directly grown on a carbon cloth substrate.The shape,appearance and structure of the sample was measured by means of scanning electron microscopy,transmission electron microscopy,X-ray diffractometry and X-ray photoelectron spectroscopy.The test results show that the crystalline cobalt-nickel oxide nanosheets are uniformly grown on the surface of the carbon cloth,and the cobalt-nickel oxide nanosheets are ultra-thin and have a porous structure,and are well formed on the carbon cloth.The ultra-thin and porous characteristics are beneficial to their catalytic activity.The carbon cloth is used as the substrate and the composition of the metal oxide increases the conductivity of the catalyst and the catalytic activity is enhanced.As an electrode and bifunction electrocatalyst for zinc-air batteries,self-supported cobalt-nickel oxide nanosheets exhibit excellent oxygen evolution performance and oxygen reduction reaction performance due to the electrical conductivity caused by the substrate and metal oxides and the ultrathin and porous structural characteristics of the nanosheets.For example,the CoNi-800/CC electrode only needs an overpotential of 277 mV to achieve a current density of 10 mA cm-2 in the oxygen evolution reaction;and the half-wave potential of CoNi-800/CC is 0.88 V and the limiting current is 3 mA cm-2 in the oxygen reduction reaction.At the same time,the liquid solid zinc-air electrode assembled by self-supported cobalt nickel oxide nanosheets has excellent practicability and stability.What's more,the synthesized catalyst was also tested for photo-assisted electrocatalytic performance.As a result,the catalyst has a good response to sunlight,and the illumination can significantly improve the activity of the material's OER and ORR under photo-assisted conditions,which is beneficial to their practical application.In view of the fact that the self-supported cobalt nickel oxide porous nanosheet is a common metal,highly active bifunctional electrocatalyst,liquid and solid zinc-air batteries are assembled.The assembled liquid zinc-air battery maintains 800 hours of stability during a continuous charge and discharge cycles with a current density of 5 mA cm-2;the assembled solid battery has an open circuit voltage of 1.475 V.In addition,the solid battery can be continuously charged and discharged for more than 12 hours at a current density of 5 mA cm-2.The combined performance of liquid and solid zinc-air batteries is comparable to that of batteries assembled by commercial Pt-C/IrO2.Therefore,self-supported cobalt-nickel oxide porous nanosheets are a very promising bifunctional catalyst. |
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