Modification Of Metal-organic Framework Derived Materials And Their Applications In High Performance Zinc Air Batteries

Zn-air battery has the advantages of high theoretical energy density,low cost and good safety performance.It has a good application prospect in both performance and economic benefit.However,the development of zinc-air batteries still faces some challenges,the main problem is the slow kinetic of oxygen reduction（ORR）and oxygen release（OER）.As we all know,platinum,ruthenium and other precious metals have been widely used as excellent ORR and OER electrocatalysts,but they are expensive and have poor stability.The key to solve this problem is to develop efficient bifunctional catalysts with low cost and stable properties.According to the investigation,heteroatom can change the local electron configuration at the doping site in transition metal and heteroatom co-doped carbon materials（TM-N-C）,thus effectively improving the reaction area and catalytic activity.Carbon materials can protect metals from acid and alkali corrosion,improve the durability of metal nanoparticles,and synergistically improve the activity of metal nanoparticles based catalysts.Metal-organic frameworks have diverse and abundant TM-N-C active sites,controllable structure and adjustable pore size,which are considered as ideal precursors for the preparation of these composites.This paper starts with the design of high-quality bifunctional electrocatalyst.Two kinds of nanomaterials were designed and synthesized using the derivatives of metal-organic framework,and their properties in electrocatalysis and zinc-air battery were tested.The main research results are as follows:（1）Metal-based materials tend to agglomerate after high temperature pyrolysis,which leads to the decrease of porosity and active sites,thus affecting the electrocatalytic performance.The polydopamine modified bimetallic Co/Zn based ZIFs（PDA@Co/Zn-ZIFs）were synthesized.Based on the volatilization characteristics of Zn at high temperature,N and Co co-doped highly porous carbon nanocubes（N/Co@HPC）were obtained after calcination at high temperature.The N/Co@HPC showed excellent bifunctional catalytic performance for ORR and OER in alkaline solution,better than Pt/C and Ru O₂ catalysts.In addition,the Zn–air battery based on N/Co@HPC electrode has an extremely long cycle life,which can cycle for more than 630 hours at current density of 10m A cm^-2.At the same time,it has good electrochemical performance of low polarization voltage and high power density.（2）In the process of pyrolysis,the content of highly active N species on the surface of ZIFs will decrease and the metal-based particles will aggregate seriously.Phytic acid was used as phosphorus source and ruthenium trichloride as Ru source,which was physically mixed with Co/Zn-ZIF and melamine.After annealing treatment at 900°C in nitrogen atmosphere,Ru-modified cobalt phosphide was dispersed in nitrogen and phosphorus co-doped porous carbon（Ru Co P@NPC）.The experimental results showed that the electrocatalytic activity of the catalyst was greatly improved thanks to a large number of nitrogen-doped high graphitized carbon,Ru_xP and Co_xP particles,the uniform dispersion of nano cobalt particles and the uniform doping of Ru.Therefore,Ru Co P@NPC has good bifunctional catalytic activity of ORR and OER,the half-wave potential is close to 0.82 V,the overpotential is 0.4 V,which are even better than Pt/C and Ru O₂ catalysts.The Zinc-air battery with Ru Co P@NPC electrode has an extremely long cycle life(101 cycles at 5 m A cm^-2;965 cycles at 10 m A cm^-2),high discharge voltage（1.33 V）,power density(116 m W cm^-2)and low polarization voltage（1.4 V）.