Study On Surface And Interface Regulation Of Oxygen Reaction Electrocatalyst In Zinc-Air Battery

With the rapid development of social economy,people's demand for efficient,green,safe and reliable advanced energy devices is becoming more and more urgent.Especially in the field of new generation portable energy storage devices and high-energy density battery energy storage,traditional battery systems have become increasingly difficult to meet people's needs in terms of energy density,safety,environmental protection,and cost.This has also stimulated people's continuous exploration and research and development of new energy devices.Among them,the zinc-air battery,Which uses zinc alloy and oxygen in the air as fuel,has attracted widespread attention due to its extremely high energy density,environmental protection,recyclability,safety and non-explosive characteristics.In fact,at the beginning of this century,a zinc-air battery has been widely used in hearing aids.However,in a broader field,such as in the field of high-power energy storage equipment that supplies power to personal portable devices(smartphones,laptops,augmented reality glasses,etc.),and provides power backup for base stations or grids,due to the lower discharge power density,recharging efficiency and service life of zinc-air batteries are temporarily unable to carry out more extensive commercial applications.The current challenges of zinc-air batteries can be mainly attributed to the slow oxygen reduction(ORR,Oxygen Reduction Reaction)and oxygen evolution reaction(OER,Oxygen Evolution Reaction)performed on the cathode air membrane electrode catalytic layer.From the perspective of electrocatalytic reaction principle,since ORR reaction and OER reaction involve four-electron transfer process,their kinetic activity is relatively slow,so the reaction rate on the electrode is greatly limited,and urgently needed advanced catalyst to accelerate the oxygen reaction.For the oxygen-catalyzed reaction on the zinc-air battery,it is a heterogeneous catalytic reaction process that exists in the three-phase reaction interface.The main reaction process can be summarized as the following four key factors:First,for the catalyst,it needs to have enough active sites at the surface/interface to fully contact the reactants,and a sufficient reaction area is the basis of everything;For oxygen reaction catalysts,the absorption and desorption energy of reaction intermediates determines the rate-limiting step of the ORR and OER reactions.Therefore,the optimized activation energy of the reaction is very important for the rapid progress of the reaction;Third,to accelerate the electrons on the surface of the catalyst.The rapid electron conduction on the surface can greatly reduce the reaction over-potential,so an efficient reaction path on the surface interface is also very important;Fourth,the oxygen reaction on the zinc-air battery requires a stable gas,solid,and liquid three-phase interface,so that the catalyst can fully interact with oxygen and ions.Thus,it is very important to construct gas and ion diffusion channels.It can be seen from the above that the physical/chemical properties of surface/interface are very important to the reactivity and stability of the zinc-air battery.Starting from the actual application requirements of zinc-air batteries,this thesis selects carbon-based and transition metal-based catalysts with abundant reserves,low prices,and easy control of surface and interface chemical properties.Through a series of surface/interface engineering strategies,the key factors that determine the electrocatalytic oxygen reaction catalyst on the zinc-air battery:the number of active sites,reaction activation energy,electron conductivity,and mass transport capacity are reasonably optimized to ensure the discharge power of the zinc-air battery,The recharging efficiency and service life have been steadily improved.This thesis aims to effectively improve the catalytic activity and stability of transition metal ORR and OER catalysts through surface and interface engineering methods such as surface anion surface modification,surface doping and electrochemical remodeling,interface coupling,and pore interface confinement engineering;In the practical application of high-power long-life zinc-air battery,combined with the actual reaction environment of the catalyst on the zinc-air battery,it provides a new idea for in-depth understanding of surface interface engnieerign strategies to optimize the electrochemical performance of transition metal catalysts.The specific content of this paper includes the following points:1.Zinc-air batteries require excellent ORR catalysts to increase their discharge power.However,the most widely reported Fe-N-C oxygen reduction catalyst has high temperature calcinations during the preparation process,which leads to serious agglomeration of iron-based particles and high active reaction sites.The author proposed a surface sulfur introduction strategy to prepare an atomic-level dispersion of Fe-Nx species on N,S co-modified carbon substrates and high-efficiency oxygen reduction electrocatalysts.Through systematic structural characterization and comparative analysis,the authors found that the introduction of sulfur can inhibit the agglomeration of Fe species due to thermal migration during high-temperature calcination,and promote the formation and high dispersion of Fe-Nx species on the carbon-based surface,which largely increased reaction active area.In addition,the systematic synchrotron radiation spectroscopy and DFT theoretical calculation analysis show that the highly dispersed Fe-Nx sites and the doped N and S can significantly optimize the electronic structure of carbon substrate,which accelerate the electron conductivity between the active sites and substrate.Besides,it can also optimize the activation energy of the oxygen reaction.The prepared S,N-Fe/N/C-CNT exhibits excellent ORR electrocatalytic activity under alkaline conditions,and the integration of this electrocatalyst into a rechargeable zinc-air battery also shows smaller charge and discharge voltage gap and higher cycle life.The work paves the way for the rational design of ORR catalysts with high reactive area and optimized reaction activation energy.2.Surface anion engineering strategy has been considered as one of the most promising chemical methods to improve catalyst performance.It can not only improve the intrinsic electron conductivity of the material through the injection of carriers,but also help to catalyze the large number of active sites during the electrochemical activation process.However,for cobalt-based materials often used as OER catalysts for rechargeable zinc-air batteries,surface anion modification tends to form stronger covalent metal-anion chemical bonds,which is unfavorable for the participation of anions in surface reconstruction.In the work of this chapter,the author synthesized a cobalt-based oxide with high OER activity by introducing a new fluoride anion surface modification method.The XAS and XPS tests of the system show that F ions with the strongest electronegativity tend to form weak metal-fluorine bonds and gain stronger ionicity,which is beneficial to the surface reconstruction of Co-based oxides.At the same time,due to the more hydrophilic surface characteristics,enhanced electron transfer capacity and the best adsorption energy of active reaction components,the OER catalytic activity of electrode materials modified with fluoride anion surface under alkaline conditions can be greatly improved.This work paves the way for enriching surface anion modification methods,understanding the surface reconstruction process of OER catalysts,and designing advanced OER electrode materials.3.In a flexible rechargeable zinc-air battery,simultaneously improving the electron conductivity of the catalyst and the ORR/OER catalytic activity is one of the most important parameters.Cobalt-based oxides are considered to have the most excellent ORR and OER dual-functional catalytic activity,but due to their lower electrical conductivity,their application in rechargeable zinc-air batteries has been greatly restricted.In this work,the author uses a ligand-assisted pyrolysis strategy to construct a nano-scale ultra-thin Co-based oxide reactive layer on a conductive carbon substrate(metallic Co/N-doped graphene substrate),thereby coupling through the interface The strategy constructs a fast electronic conduction path from a highly conductive substrate to a rich active site CoOx.The X-ray absorption spectrum characterization and electronic energy spectrum characterization analysis of the system show that the strong coupling between the metal Co/N-doped graphene substrate and the ultra-thin CoOx layer facilitates the rapid transfer of electrons from the conductive substrate to the reactive site,Thereby accelerating the electrocatalytic reaction process.The synthesized electrocatalyst has excellent ORR/OER catalytic activity and exhibits extremely high power output capability in the test of flexible zinc-air battery.The interface coupling strategy provides a new way to design electrocatalysts for rechargeable zinc-air battery systems with optimized conductivity and reactivity.4.The large-scale zinc-air battery with high energy density,environmental protection,safety and low price brings great convenience to the energy security backup and power storage of the future power system.However,the fragile stability exhibited by most oxygen reduction catalysts under actual battery high current output conditions severely limits their further commercial applications.In this work,from the perspective of the principle of the three-phase reaction interface of a zinc-air battery,the author uses the nanopore interface confinement strategy to prepare high-efficiency ORR cobalt-based nanoparticles.Synchrotron radiation characterization and molecular dynamics simulation analysis show that benefiting from the water blocking effect of confined nanopores,the highly active cobalt cluster electrocatalyst in specific nanopores has a stable three-phase reaction interface,and has a stable three-phase reaction interface with the pore interface.Strong coupling effect realizes the coordinated optimization of electron conduction,oxygen diffusion and ion migration in the electrocatalytic process.The zinc-air battery equipped with this catalyst exhibits the best stability under high current density discharge conditions(>90 h@100 mA cm-2)and has a higher power than most reported non-noble metal catalysts Density(peak power density:>300mW cm-2,specific power:500 Wgcat-1).This work makes it possible to control the transport behavior of gases,ions,and electrons through interface engineering,and to prepare zinc-air batteries with ultra-high power output and high stability.