【作者】 刘波；

【导师】 李箭；

【作者基本信息】 华中科技大学 ， 材料学， 2022， 博士

【摘要】 固体氧化物燃料电池（solid oxide fuel cell,SOFC）是一种能将燃料中的化学能直接转化为电能的能源转化装置,具有高效、清洁和燃料选择范围广等优点。传统SOFC的工作温度较高,导致材料选择、密封、运行和维护困难且成本过高,限制其商业化发展。因此,降低SOFC工作温度已成为当今的趋势。质子传导型固体氧化物燃料电池（H-SOFC）具有载流子传导活化能低和阳极燃料浓度高等优势,在中低温下具有更广阔的应用前景。H-SOFC阴极材料需要同时具有质子、氧离子和电子的三重导电能力,以及良好的稳定性。当前的H-SOFC阴极材料存在热膨胀系数大、质子吸收浓度低和质子体传导速度慢等问题。针对这些挑战,本文采用表面修饰和低电负性元素掺杂等方法,先后制备了三种复合或单相三重导电阴极材料。经过系统研究,本文得到以下主要成果:（1）将PrBa Co₂O_5+δ（PBC）浸渍在Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O₃（BZCYYb）骨架上,获得了三重导电复合阴极材料PBC@BZCYYb,并研究PBC浸渍量对电极性能的影响。当PBC浸渍量为36wt%时,复合阴极性能最优。电极性能的提升来源于PBC对阴极氧还原能力的增强作用。当浸渍量更高时,较差的PBC质子传导能力和较低的阴极孔隙率导致电极性能降低。以最优浸渍量的PBC@BZCYYb作为阴极时,单电池在750℃的峰值功率密度为0.49 W cm^-2。（2）为了增强PBC的质子传导能力,从降低阳离子电负性的角度,设计了A位掺杂Ca,B位掺杂Zn的钴基双钙钛矿材料PrBa_0.9Ca_0.1Co_2-xZn_xO_5+δ（x=0、0.05、0.1和0.15,简写为PBCCZy,y=00、05、10和15）。Zn掺杂会增加材料的氧空位浓度和晶格氧结合能,前者有利于质子的吸收,而后者则相反,导致随着y增加,PBCCZy的质子吸收能力先下降后上升。PBCCZ15的氧表面交换、氧体传导和质子体传导能力均高于PBCCZ00。Zn掺杂并不能降低PBCCZy的平均热膨胀系数,均为21.3×10^-6 K^-1左右。采用以PBCCZ15和BZCYYb形成的复合阴极时,单电池在700℃的峰值功率密度为0.89 W cm^-2,并在600℃和400 m A cm^-2工作条件下,50 h内性能无明显衰减。此研究表明降低材料的阳离子电负性,能够有效提高其质子吸收和传导能力。（3）为了获得低热膨胀系数的单相三重导电阴极材料,设计了低电负性元素K掺杂的单相铁基双钙钛矿材料PrBa_1-xK_xFe_0.9Zn_0.1O_5+δ（x=0和0.1,简写为PBKFZy,y=00和10）。K掺杂能同时增加材料的氧空位浓度和降低晶格氧结合能,有效提高材料的氧表面交换、氧体传导和质子吸收与传导能力。PBKFZ10最大质子吸收浓度为6mol%,高于PBKFZ00的2mol%。材料的平均热膨胀系数从18.3×10^-6 K^-1降低至16.1×10^-1 K^-1。以单相PBKFZ10为阴极时,单电池在700℃的峰值功率密度可达到1.40 W cm^-2,其为无钴阴极质子传导型SOFC的最高输出功率。该单电池在600℃和400 m A cm^-2的工作条件下,75 h内性能无明显衰减,表明PBKFZ10在中低温具有优异电化学性能和稳定性。更多还原

【Abstract】 Solid oxide fuel cell（SOFC）is an energy conversion device that converts the chemical energy stored in fuels directly to electric power with the advantages of high efficiency,low emission,and fuel flexibility.However,the high working temperature（above 800℃）restricts the commercialization of traditional SOFC,due to the difficult material selection,sealing,operation,maintenance,and high cost.Decreasing the working temperature is the current research trend.The proton-conducting solid oxide fuel cell（H-SOFC）has the advantages of low activation energy for carrier conduction and high fuel concentration in the anode,and shows broader application prospects at medium-to-low working temperatures.The H-SOFC demands a stable cathode with triple conductivity of protons,oxygen ions,and electrons at the same time.However,the states-of-the-art cathode could not meet these requirements,most of them present one or some of the following drawbacks including mismatched CTE with electrolyte,low proton absorption concentrations,and slow proton conduction.In this work,three kinds of composite or single-phase cathode materials were proposed and investigated to overcome these problems by surface modification and low-electronegativity element doping.The conclusions are made as follows:（1）The triple conducting cathode,PrBa Co₂O5+δ@Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ（PBC@BZCYYb）,was prepared by impregnating the PBC particles on the surface of BZCYYb skeleton.The effect of PBC impregnation amount on the electrode performance was investigated.The loading of PBC with 36 wt%boosted the electrochemical performance of cathode best with its abislity to improving oxygen reduction reaction.However,higher PBC loading reduced the performance because it reduced the porosity and proton transportation ability of cathode.The peak power density of the anode-supported single cell was 0.49 W cm^-2 at 750℃ with the optimal loading of PBC@BZCYYb as cathode.（2）Zn-doped PrBa_0.9Ca_0.1Co_2-xZn_xO5+δ（x=0,0.05,0.1,and 0.15,designated as PBCCZy,y=00,05,10,and 15）were prepared and investigated,as it is recognized that doping lower cation electronegativity elements could improve proton transportation ability of PBC.The Zn-doping increased the concentration of oxygen vacancy and binding energy of lattice oxygen for PrBa_0.9Ca_0.1Co₂O5+δ,which the former was in favor of the uptake of proton and the latter was un-favor.Therefore,the proton uptake ability of PBCCZy firstly decreased and then improved with the Zn contents increased.Besides,the rate of surface exchange and bulk transportation for oxygen ion and proton of PBCCZ15 was much higher than that of PBCCZ00.The Zn-doping could not reduce the CTE of PBCCZy,all around21.3×10^-6 K^-1.The peak power density of single cell reached 0.89 W cm^-2 at 700℃ with PBCCZ15-BZCYYb as cathode material.The electrochemical performance of single cell could keep stable within 50 h under 400 m A cm^-2 at 600℃.This work confirmed that reducing the cation electronegativity of material could effectively improve its proton absorption and transportation ability.（3）K-doped PrBa_1-xK_xFe_0.9Zn_0.1O₅₊δ（x=0 and 0.1,designated as PBKFZy,y=00 and10）were prepared and investigated to obtain a single-phase triple conductive cathode material with low CTE.K-doping could simultaneously increase the concentrations of oxygen vacancy and reduce the binding energy of lattice oxygen,effectively improving the rate of surface exchange and bulk transportation for proton and oxygen ion of PBKFZ00.The maximum proton absorption concentration of PBKFZ10 was 6 mol%,higher than 2mol%of PBKFZ00.Besides,the CTE of PBKFZ00 was decreased from 18.3×10^-6 K^-1to16.1×10^-1 K^-1 by K-doping.The single cell with PBKFZ10 as cathode showed a peak power density with 1.4 W cm^-2 at 700℃,which was the highest performance among Co-free cathode materials in literature.the single cell operated stably for 75 h under 400 m A cm^-2at 600℃,indicating a good electrochemical performance and stability at medium and low temperatures.更多还原