Controlled Preparation Of Zeolite Imidazole Frameworks And Their Derivatives For Zinc-air Batteries

In recent years,the excessive consumption of traditional fossil energy has led to serious atmospheric and water pollution.Green sustainable energy sources as an effective alternative to fossil energy（such as hydrogen,etc.）have draw widespread attention of researchers.Rechargeable zinc-air battery is a new type of electrochemical energy storage and conversion device.It can directly use the oxygen in the air to react during operation,and it has the advantages of high energy density,good safety and low price,results in the broad prospects in the field of sustainable energy.However,for zinc-air batteries,the kinetics of the oxygen reduction（ORR）reaction and the oxygen evolution（OER）reaction are sluggish,the discharge-charge potential interval is large and the energy utilization rate is low,the existing noble metal oxygen reaction catalysts（Pt,Ir）are expensive.Which severely limited the practical application of zinc-air batteries in large-scale energy storage.Therefore,designing and developing catalysts with high efficiency and low cost has important practical significance.Zeolite imidazole frameworks（ZIFs）,as one member of metal organic frameworks（MOFs）with similar zeolite topologies,own large specific surface area,adjustable pores,controllable metal ions/clusters and ligands,which resulting in they diplay widely application potential in energy storage and conversion.Unfortunately,due to their poor conductivity and mostly three-dimensional structure,ZIFs materials are insufficient in catalytic active sites and have low intrinsic activity.Currently,the hot topic of research on ZIFs is mainly focused on ZIF-derived materials.ZIF-derived materials are obtained for high-temperature calcination of precursors for OER and ORR catalysis,but this process is an energy-extensive consumption process,metal ions are easily agglomerated and lower productivity,so it is not profitable to large-scale preparation and application.Therefore,to design and prepare the low-dimensional ZIF and ZIF-based derivatized oxygen catalysts with high-performance via a simple and efficient method is important for the large-scale application of zinc-air batteries.This thesis takes ZIFs as the research object.It carries out related work on the metal element doping of low-dimensional ZIF materials,the controllable preparation and formation mechanism of ZIF-based materials and the performance of rechargeable zinc-air batteries.The specific research contents are as follows:（1）Macrostructured ZIF-derived nanosheets are used to assemble hydroxide/oxide hierarchical structures by lye immersion.The composition and morphology of the precursor bimetallic ZIF materials are regulated by optimizing the type and proportion of metal salts.The formation mechanism of hydroxide hierarchical structure during immersion in alkali is investigated.The electrocatalytic OER performance and zinc-air battery performance of ZIF-derived Co（OH）₂ multistage structure are further characterized.The results show that the ZIF-derived Co（OH）₂ hierarchical structure has excellent electrocatalytic OER performance.When the current density is 10 mA·cm^-2,the overpotential of the Co（OH）₂ hierarchical structure is only 267 mV.The tafel slope is only 62 mV·dec^-1,and it has good stability(constant current polarization test at a current density of 10 mA·cm^-2,and the performance hardly decreases after 12 hours).Zinc-air battery whose air cathode assembled by Co（OH）₂ hierarchical structure mixed with commercial Pt/C has a small discharge-charge potential interval and excellent charge-discharge cycle stability（after²70 h,the interval of discharge-charge potential hardly becomes large）.The excellent performance of Co（OH）₂ hierarchical structure is mainly attributed to the hierarchical structure of Co（OH）₂ nanosheet assembly,which effectively inhibits the stacking between nanosheets and makes full use of the active site of the catalyst.The one-dimensional rod structure assembled by two-dimensional nanosheets significantly increases the transfer rate of electrons/charges during the catalysis process.（2）A metal-doped ZIF nanosheet arrays is prepared on nickel foam（NF）by a simple one-step hydrothermal method,and the multifunctional catalysis of ZIF nanosheets is realized.The influence of metal doping on the morphology and structure of ZIF materials is investigated.On the basis of this,the influence mechanism of metal doping on the multifunctional catalysis of ZIF materials was investigated by electrochemical performance test.The results show that the Mo-doped MnNiMo-NF nanosheet arrays has excellent electrocatalytic OER,ORR and HER activity,which is much better than the undoped metal MnNi-NF nanosheet arrays,and its OER catalytic stability is excellent(After constant current polarization for about 300 h at a current density of 10 mA·cm^-2,the overpotential increases only about 9 mV).The MnNiMo-NF nanosheet arrays grown on nickel foam is directly used as a binderless self-supporting air cathode in a rechargeable zinc-air battery.The discharge-charge potential interval of the zinc-air battery is smaller(when the current density reaches 50 mA·cm^-2,the potential interval is 1.181 V,while the potential interval of MnNi-NF is 1.816 V),and the maximum discharge power density is larger(56.74 mW·cm^-2,while the MnNi-NF is 20.37 mW·cm^-2)and has good stability.The excellent multifunctional catalytic performance of Mo-doped MnNiMo-NF nanosheet arrays is mainly attributed to the change of the coordination environment of Mn and Ni in ZIF nanosheets after Mo doping,the binding energy is improved,and the number of catalytic active sites are increased.The nanosheet array structure effectively suppresses the mutual stacking between the sheets and has a high utilization rate of catalytic active sites.The self-supporting electrode has a strong interaction between the nanosheets and the nickel foam during the reaction process.The bonding ability makes the electrode’s resistance smaller,and also makes the electron and charge transfer speed faster.