Preparation,Characterization And Properties Of LaFeO₃ Perovskite Electrocatalysts For Lithium-oxygen Battery

Non-aqueous lithium-oxygen battery is a promising candidate for next generation energy storage due to its high specific capacity.Now its research still stay at fundamental exploration,and one of the most important problems is focused on the sluggish oxygen reaction kinetics.During the discharge process,masses of isolated products which are mainly consisted of lithium peroxide deposit on oxygen electrode,hindering the electronic transfer,leading to large polarization and limiting the capacity and cycle stability of the Li-O₂ battery.Designing high efficient bifunctional electrocatalysts is considered to be one of the most effective strategies,including the optimized design of cathode structures and the enhancement of the oxygen reduction reaction?ORR?and the oxygen evolution reaction?OER?kinetics.In this paper,LaFeO₃ was chosen as the main research object,and in order to investigate LaFeO₃'s inherent catalytic activity,LaFeO₃ nanoparticles?NP-LaFeO₃?were firstly prepared,and their electrocatalytic activity were characterized via electrochemical technology.Subsequently,in view of poor conductivity and slightly weak catalytic activity of the LaFeO₃,compound modification method was taken to further optimize its electrocatalytic activity.Based on this strategy,reduced graphene oxide-LaFeO₃?RGO-LaFeO₃?and RuO₂/LaFeO₃ nanocomposite electrocatalysts were explored in lithium-oxygen battery,their morphologies and structures were observed by characterization technologies such as XRD,SEM,FTIR,N2 sorption isotherms,etc.Besides,electrochemical test and discharge product characterization results were combined to analysis mechanism of catalytic reaction.Meanwhile,all elecrtocatalysts were applied in Li-O₂ batteries to test the battery performances.The main research achievements were obtained as follows:?1?NP-LaFeO₃ was prepared via Pechini method,and three vital experimentfactors were studied in detail.When pH value of reaction solution was 9,calcination temperature was 900 ? and the precursor was calcined directly at high temperature without grinding before,LaFeO₃ nanoparticles with rod morphology composed of some sphere-like particles were successfully abtained.The Li-O₂ battery with NP-LaFeO₃ electrocatalyst sustained 40 cycles at 500 mAh·g-1,and showed better electrical energy efficiency than acetylene black catalyzed battery.?2?A new synthesis method was developed to get RGO-LaFeO₃ nanocomposite electrocatalyst in situ.Chronoamperometry and linear sweep voltammetry test results demonstrated that RGO-LaFeO₃ exhibited enhanced ORR and OER activity compared with RGO and NP-LaFeO₃ electrocatalysts.Li-O₂ battery with RGO-LaFeO₃ electrocatalyst could maintain 70 reversible cycles with a limited capacity of 500 mAh·g-1 at a rate of 100 mA·g-1.Meanwhile,the formation and decomposition of Li₂O₂ at the specific discharge or charge state was characterized via the SEM and XRD tests of the oxygen electrode.These excellent performances are mainly attributed to two aspects:on one side RGO-LaFeO₃ nanocomposite electrocatalyst shows synergistic effect between RGO and LaFeO₃ nanoparticles,on the other hand the electrocatalyst possesses three-dimensional conductive heterogeneous structure with both meso and macro pores,which is good for discharge product storage,electronic transfer and oxygen diffusion.?3?BLF micro-sphere decorated RuO₂ nanoparticles were synthesized by a combined method of hydrothermal reaction and impregnation.Chronoamperometry and linear sweep voltammetry tests were conducted to study its electrochemical property,After the decoration of the RuO₂ nanoparticles,the OER activity of the RuO₂/BLF was obviously enhanced.Meanwhile,the Li-O₂ battery with RuO₂/BLF was operated with 500 mAh·g-1 capacity at a current density of 100 mA·g-1,it could maintain 65 stable cycles and deliver a charge-discharge overpotential of 0.90 V.SEM and XRD characterization of the oxygen electrode demonstrated that RuO₂/BLF electrocatalyst could facilitate the formation of the Li₂O₂ with small size during the discharge process,and Li₂O₂ mainly stored in the mesopores on the surface of LaFeO₃ sphere or in the pile pores between LaFeO₃ nanoparticles,so that catalytic active sites could be retained to facilitate the decomposition of Li₂O₂ during the charge process.The research work of this paper extended the application of perovskite type electrocatalyst for lithium-oxygen battery,and privided new strategies for constructing ORR and OER bifunctional electrocatalyst.