Construction And Properties Of Perovskite/Graphite Felt Composite Electrode For Vanadium Redox Flow Battery

As one of the most potential energy storage technologies,vanadium redox flow battery(VRFB)has the virtues of flexible design,high safety and long lifetime.Graphite felt electrode is key to the capacity and efficiency of VRFB.However,its high graphitization causes poor hydrophilicity,insufficient active sites,and weak electrocatalysis.Perovskite has been used in electrocatalysis due to variety,flexible regulation,low cost and easy synthesis.Herein,perovskite catalysts for vanadium redox reactions were developed and tuned based on the composition and structure.The activity of the composition,crystal,electronic structure and characterization of perovskite on vanadium redox reactions was systematically studied.The perovskite/graphite felt composite electrodes were constructed to improve the property of VRFB.In VRFB,the anode kinetics was slow and accompanied by side reactions.IVB group metal compounds showed catalysis for V3+/V2+ reaction.SrBO3(B=Ti,Zr,Hf)perovskite catalyst was developed,where B metal was used to tune the electronic structure and characterizable properties.The catalytic mechanism of SrBO3 for V3+/V2+ reaction was explored by experiments and calculation.As B atomic number increased,the oxygen defect increased,which boosted the adsorption of V3+/V2+.Meanwhile,the reduction of B-O bonding orbital hybridization boosted the charge transfer of V3+/V2+ reaction.However,the large particles and deformed crystals of SrHfO3 reduced its catalysis.SrZrO3 stood out for catalysis due to high hydrophilicity,large surface area,and desired crystal.SrZrO3 was used to modify graphite felt(GF)and construct SrZrO3/GF electrode.The cell using SrZrO3/GF as negative anode showed an energy efficiency(EE)of 63.2%at 300 mA/cm2 and was 15%higher than the blank one at 200 mA/cm2.This laid the foundation for the perovskite regulation for activity required of vanadium redox reactions in structural and compositional flexibility.Zr-O bonding has the bifunctional catalysis for vanadium redox reactions.The catalysts of AZrO3(A=Ca,Sr,Ba)perovskite were developed with the center of Zr.The effects of A metal ionic radius on the electronic structure,characterization and electrocatalysis of AZrO3 were explored.As A metal ionic radius increased,the grain size and agglomeration of nanoparticles decreased.SrZrO3 and BaZrO3 exhibited larger surface area.Besides,AZrO3 showed good hydrophilicity in the increasing order of SrZrO3,BaZrO3,and CaZrO3.AZrO3 had intrinsic catalysis for both V3+/V2+and VO2+/VO2+ reactions in order of SrZrO3>BaZrO3>CaZrO3,and SrZrO3 had the best activity owing to ideal crystal,and large surface area and good hydrophilicity.It was used as a bifunctional catalyst for GF to improve the EE of cell.The EE of modified cell is 85%and 56%at 50 and 250 mA/cm2,respectively.At 200 mA/cm2,SrZrO3 increased 7%of EE compared to the blank one.Perovskites with lanthanide at A site are abundant and have large space for regulation.LaBO3(B=V,Cr,Mn,Fe,Co)perovskites were obtained by sol-gel way.The effects of the same periodic metal on the stability,crystal,electronic structure and characterization properties of LaBO3 were studied.As the B metal activity increased,the stability decreased.LaBO3(B=V,Cr,Mn)was applied to vanadium redox reactions.They boosted the V3+/V2+and VO2+/VO2+ reaction kinetics in order of Mn,Cr and V.The catalysis was mainly attributed to the B-O bonding and the activity of perovskite structure,which promoted vanadium ion adsorption and charge transfer.The EE of the cell using graphite felt/LaMnO3 reached 60%at 300 mA/cm2.At 200 mA/cm2,the EE of the modified cell increased by 20%compared with blank one.Density functional theory also elucidated the intrinsic catalytic mechanism of LaBO3 in terms of adsorption and charge transfer.The stoichiometric Sr and Ce doping at A site of LaMnO3 was used to bidirectionally tune the activity of LaMnO3 for V3+/V2+and VO2+/VO2+ reactions.The evolution of Mn and O chemical state along different directions was studied,and the effect of doping amounts on the electronic structure,characterization property and electrocatalysis of LaMnO3 was explored.Sr doping improved the activity of LaMnO3 for V3+/V2+reaction.Sr and Ce doped LaMnO3 achieved the best catalysis at doping ratios of 20%and 10%,respectively.Sr and Ce-doped LaMnO3 was used as the negative and positive catalysts respectively to improve the property of cell.Compared with the blank one,especially at 150 mA/cm2,the EE of the bidirectional modified cell was increased by 17.3%.At 300 mA/cm2,the modified cell provided an EE of 66.5%,while the blank one was out-of-work.Figure 101;Table 20;Reference 185...