Design Of ZIF-67 Derived Continuous Carbon Network For Zn-Air Battery

With the increasing consumption of fossil fuels,serious ecology deterioration and ever-increasing energy demand require research communities to explore sustainable electrochemical energy devices and systems.Among various available energy technologies,Zn-air batteries（ZABs）have gained increasing popularity due to the low cost,environmental harmony,and high theoretical energy output.However,ZABs face some scientific and technological problems,especially poor stability and low power density,which are mainly the consequence of the sluggish kinetics in the cathodic reaction.Therefore,the most important issue is developing bifunctional oxygen electrocatalyst for air electrode,which can catalyze both oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）for discharging and charging process in rechargeable batteries.Heretofore,Pt-based catalysts are the most active for ORR,while Ir/Ru compounds are state-of-the-arts candidates for OER.Nevertheless,high cost and poor stability of the noble-metals limit their large-scale practical implementation.Moreover,due to monofunctional character,these precious single-component catalysts are often mixed to achieve bifunctional activity for the rechargeability of ZABs.Consequently,non-precious candidates with earth-abundant element are attracting extensive attention for developing low-cost and high-performance bifunctional alternatives for the rechargeable ZABs.Metal-organic frameworks（MOFs）derivatives show the potential bifunctional catalytic activity of ORR and OER in view of their intriguing advantages of abundant active site,conductivity,and advanced porous nanostructures.Nevertheless,their performances in ZABs still need to be improved,as their particle nature of MOFs derivatives in nanoscale level is not sufficient enough for effective reactant transfer and electrolyte diffusion in ZABs devices.Based on ZIF-67,we rationally design efficient and bifunctional oxygen electrocatalyst with a continuous structure at the air electrode level.NCNTM and FNCF are prepared to overcome the disadvantages of unsufficent mass transfer and agglomeration and improve the performance of ZABs.The main contents and achievements of this dissertation are as follows:（1）In chapter three,we prepare a three-dimensional continuous nitrogen-doped carbon nanotube matrix for oxygen electrocatalysis in rechargeable Zn-air batteries.Thanks to the synergistically advantageous features of abundant metal-nitrogen-carbon active sites in the continuous matrix architecture,this NCNTM exhibits outstanding bifunctional activity and stability for oxygen electrocatalysis.Specially,the rechargeable battery assembled by NCNTM achieves a remarkable open-circuit voltage of 1.50 V and outstanding power density of 220 m W cm^-2,together with remarkable cycling stability of over 1600 h at 5 m A cm^-2.Moreover,the flexible solid-state battery delivers a power density of 176 m W cm^-2,which are capable to power 56 LED and smartphone.The study not only provides an efficient bifunctional oxygen electrocatalyst but importantly paves significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies（2）In chapter four,based on ZIF-67,we further prepare flexible nitrogen-doped carbon film hybrid by the Zn template,as free-standing bifunctional oxygen electrocatalyst for rechargeable ZABs.This FNCF hybrid exhibits exceptional bifunctional activity and stability for oxygen electrocatalysis.Additionally,FNCF assembled ZABs without agglomerant delivers a remarkable open-circuit voltage of 1.48 V and outstanding power density of 185m W cm^-2,together with remarkable cycling stability of over 1200 h at 10 m A cm^-2.Moreover,the flexible solid-state battery delivers a power density of 160 m W cm^-2 and and a stable discharge voltage even underbending condition.This work paves a valuable way for designing free-standing integrated air cathodes for Zn–air batteries and others energy conversion and storage technologies.