Study On Catalytic Performance And Mechanism Of Cobalt Molybdate In Lithium Air Batteries And Photo-fenton System

Due to its catalytic activity,transition metal molybdate is widely used in the fields of photo-Fenton,Lithium-ion batteries,supercapacitors and sensors.The common form of molybdate is ABO₄（A:Co,Ca,Cu,Zn,Ni）,among which CoMoO₄has the advantages of adjustable transition metal valor and morphology,which has a potential application prospect in the field of photo-Fenton degradation of dye wastewater and Lithium air batteries（LABs）.There are two crystal structures of CoMoO₄,namelyα-CoMoO₄andβ-CoMoO₄.In this paper,α-CoMoO₄was selected as the catalyst of persulfate（PDS）photo-Fenton system to degrade Congo red,andβ-CoMoO₄was selected as the positive catalyst of LABs for electrochemical performance test.The properties and mechanism of CoMoO₄catalyst were studied.α-CoMoO₄ nanobulk were prepared by the coprecipitation-calcination method,andβ-CoMoO₄nanotubes/rods were prepared by the electrospinning-calcination method.The structure,morphology and physicochemical properties of CoMoO₄were analyzed through SEM,TEM,XRD,XPS and Raman.Usingα-CoMoO₄as PDS active catalyst for the degradation of Congo red（CR）,the best catalyst was selected to study the mechanism and path of CR degradation,the electrochemical performance ofβ-CoMoO₄positive catalyst at different calcination temperatures was studied,and the best catalyst was selected to study the mechanism of release charging.The main research conclusions are as follows:（1）Preparation and characterization ofα-CoMoO₄photo-Fenton catalyst.Through the coprecipitation-calcination method（calcination temperature is 800,900 and 1000℃;named CMO-8,CMO-9 and CMO-1）,α-CoMoO₄nanobulk were prepared,and their physicochemical properties were analyzed by SEM,XRD,Raman,FTIR and UV-Vis DRS.The results show that wolframiteα-CoMoO₄is composed of nanosheets stacked into nanobulk.The structure of the nanosheets is loose and there are many gaps,which can improve the exposure degree of active sites.The band gap width is 1.93 e V.The unique physical and chemical properties ofα-CoMoO₄enable it to achieve ideal results in photo-Fenton degradation of CR.（2）Photocatalytic properties and mechanism ofα-CoMoO₄.Selecting CR as the target pollutant,the photo-Fenton catalytic performance ofα-CoMoO₄was studied,the best catalyst was selected,and the catalytic mechanism of UV-Vis/PDS/CMO-8 system was explored.The results show that:When the concentration of CR was 100 mg L^-1,the concentration of CMO-8was 0.8 g L^-1,and the concentration of PDS was 9.8×10^-6mmol/L,the removal rate of CR by UV-Vis/CMO-8 system reached 63.68%（t=240 min）.The removal rate of CR by UV-Vis/PDS system was only 41.34%（t=25 min）,and the removal rate of CR by UV-Vis/PDS/CMO-8system was 96.29%（t=25 min）.It can be seen that CMO-8 has a good activation effect on PDS in UV-Vis/PDS/CMO-8 system,and the activation performance of CMO-8 on PDS is mainly due to the electron shuttle effect of Co²⁺/Co³⁺.The reactive oxygen species（ROS）ofα-CoMoO₄photo-Fenton system were determined by using methanol,tert-butyl alcohol,ammonia oxalate,histidine and p-benzoquinone as trapping agents.The results showed that·OH,SO₄^-·,O₂^-·,¹O₂and h⁺ROS existed in the photo-Fenton system.The ROS contribution rate was in the order of·O₂^->·OH>SO₄^->h⁺>¹O₂,and CR was degraded through free radical and non-free radical pathways.（3）Preparation and characterization ofβ-CoMoO₄positive catalyst.Electrospinning-calcination method is adopted（calcination temperature is 400,500 and 600℃.Those were named CMO-4,CMO-5 and CMO-6 respectively.）,and the physical and chemical properties ofβ-CoMoO₄nanotubes/rods were analyzed through SEM,TEM,XRD and Raman.The results showed that the schetungsten structureβ-CoMoO₄was a tube/rod shape with a diameter of about 50～240 nm,and the tube/rod size distribution was relatively uniform.The tube structure could provide space for the growth of discharge product Li₂O₂,which could significantly improve the electrochemical performance of LABs.（4）Electrochemical properties and mechanism ofβ-CoMoO₄.Usingβ-CoMoO₄as LABs positive catalyst,the electrochemical performance under different conditions were tested,the best performance electrode was selected,and the catalytic mechanism of the electrode was analyzed.The results showed that:When the air humidity was less than 30%,the specific capacity was 600 m A g^-1,and the current density was 200 m A g^-1,500 m A g^-1and 1000 m A g^-1,the CMO-4 electrode showed excellent electrochemical performance,achieving 164,247 and270 cycles,respectively.166 cycles were achieved with specific capacity of 1000 m Ah g^-1and current density of 500 m A g^-1.When the air humidity is greater than 30%,the cutoff capacity is600 m Ah g^-1and the current density is 500 m A g^-1,the CMO-4 electrode can achieve 156cycles,and the CMO-4 can achieve 433 cycles in the oxygen atmosphere.The end of the life of LOBs is the accumulation of discharge products and byproducts leading to catalyst inactivation,and the end of the life of LABs is also effected by the water in the air,water vapor corrosion of lithium metal cathode seriously affects the life of LABs.The development of LABs positive electrode materials helps to solve the greenhouse effect and other ecological environmental problems caused by the use of fossil fuels and promote the development and use of clean energy.