阴极材料La_(0.7)Sr_(0.3-x)Ca_xCo_(0.8)Fe_(0.2)O_(3-δ)的晶体结构和性能

Research on properties and crystal structures of La_(0.7)Sr_(0.3-x)Ca_xCo_(0.8)Fe_(0.2)O_(3-δ) as the cathode for ITSOFCs

使用硝酸盐,氢氧化钠和碳酸钠为沉淀剂,共沉淀法合成了中温固体氧化物燃料电池阴极材料La_(0.7)Sr_(0.3-x)Ca_xCo_(0.8)Fe_(0.2)O_(3-δ)(x=0.05、0.10、0.15、0.20)的粉料并研究了粉料的各种性能。结果表明,前驱体800℃煅烧3h形成粉料具有六角晶系钙钛矿结构;Ca2+和Sr2+双掺杂取代La3+进入晶格后,随着Ca2+含量x增加,La_(0.7)Sr_(0.3-x)Ca_xCo_(0.8)Fe_(0.2)O_(3-δ)晶胞a轴方向缩短c轴方向拉长,晶胞体积减小;且1200℃烧结3h后所有样品电导率在降低。温度升高到490℃,掺杂样品的电导率出现最大值,温度继续升高晶格氧逸出导致电导率降低。当x=0.10和0.15时,阴极材料电导率在500～650℃范围内基本相等且高于700S/cm,并与Ce0.8Sm0.2O2热性能的表现一致,且两者阴极材料在650℃时,所组装单电池的输出功率明显大于350mW/cm2。

The powders of La0.7Sr0.3-xCo0.8Fe0.2O3-δ（x=0.05,0.10,0.15,0.20） as a cathode materials for intermediate temperature solid oxide fuel cells have been synthesized by a chemical co-precipitation method with metal-nitrates and mixed alkali（ NaOH and Na2CO3） as the starting materials and precipitator. The current-voltage（J-U） and current-power （J-P）characteristics for the fuel cell using the synthesized powders as the cathode at the temperatures from 500 ℃ to 650 ℃ were determined by using the equipment for measuring current and voltage under variable loads. The XRD results show that all co-precipitations calcined at 800 ℃ for 3 h have a rhombohedral perovskite structure after the replacement of Sr^2＋and Ca^2＋on the A-site for La^3＋, and that the increasing of Ca^2＋content in the La0.7Sr0.3-xCaxFe0.2O3-δ compounds cause not only the shortening of a axle direction and the prolongation of c axle direction in crystal cell parameters, but also the decrease of the crystal cell volume, and also lead to the lower of the electrical conductivity of all doped specimens sintered at 1 200℃ for 3 h as a function of temperature from 300 ℃ to 800 ℃ in air. It shows that the electrical conductivity of all doped samples increases with temperature up to about 490 ℃,and then decreases due to the loss of lattice oxygen, and is higher than 400 S/cm from 500 ℃ to 650℃, especially the electrical conductivity of La0.7Sr0.3-xCaxCo0.8Fe0.2O3-δ can basically be equal, and be up to 700 S/cm with x=0.10 and 0.15. Then the power density output of the single fuel cell using the prepared powders with x=0.10 and 0.15 as the cathode was higher than 350 mW/cm2 at 650 ℃ and the thermal behavior obtained using TMA-840 between La0.7Sr0.15Ca0.15Co0.8Fe0.2O3-δ cathode and Ce0.8Sm0.2O2 electrolyte were basically consistent from 500 ℃ to 650 ℃.