【作者】 李强；

【导师】 范勇；

【作者基本信息】 哈尔滨理工大学 ， 材料学， 2007， 博士

【摘要】 固体氧化物燃料电池（SOFC）是一种具有高效、环境友好等优点的发电装置。作为SOFC重要组成部分的阴极材料一直是人们研究的重点。传统的SOFC阴极材料多为钙钛矿结构ABO₃型氧化物,如La_1-xSr_xMnO₃ （LSM）等,这类材料在1000 oC时极化电阻仅为几欧姆,但随着工作温度的降低,其极化电阻猛增到几千欧姆。为此,寻求新的能在中温条件下使用的阴极材料成为中温燃料电池研发的重要任务。类钙钛矿结构A₂BO₄型氧化物是一类同时具有电子导电和离子导电的混合导体,这类材料在氧透过性、热化学性能、电化学性能以及氧的扩散和表面交换能力等方面显示了明显的优势。与传统的ABO₃型SOFC阴极材料相比较,A₂BO₄型氧化物的热膨胀系数数值较小,并且与传统的固体电解质钇稳氧化锆（YSZ）和Ce_0.9Gd_0.1O_1.9（CGO）有很好的热匹配性。此外,这类材料在中温区间具有较高的电导率,这对阴极材料来讲是极为有利的。以上这些都充分说明了A₂BO₄型复合氧化物是一种潜在的中温固体氧化物阴极材料。有关未掺杂或B位掺杂的A₂BO₄型复合氧化物电化学性能已经有了一些报道,但对于A位掺杂的A₂BO₄型复合氧化物电化学性能研究鲜有报导。本论文采用甘氨酸-硝酸盐法制备了A位Sr掺杂的A₂BO₄型中温固体氧化物燃料电池阴极材料Ln_2-xSr_xMO₄ （Ln=La, Nd, Sm; M=Ni, Cu）。考察了电极材料与电解质材料在高温时的化学相容性;研究了烧结温度对电极的微观形貌及电化学性能的影响,结果表明,烧结温度过高或过低都会导致电极极化面电阻的增加,当电极的烧结温度适中时,电极表面粒子有一定的烧结连接,并且有一定的多孔结构,电极的极化面电阻达到最小值。为了考察电极反应动力学,研究了电极的极化面电阻随测试温度和氧分压的变化情况,来确定电极上的速率反应步骤。结果发现,电极反应的速率控制步骤主要有电荷的迁移过程、氧的解离和吸附过程以及氧离子从三相界面向电解质的转移过程,在不同的温度与氧分压下电极可能有着不同的速率控制步骤。其中,Sr掺杂的La₂CuO₄电极具有很好的化学稳定性以及较高的电催化活性,与电解质CGO在1000 oC烧结144小时后,经XRD检测发现二者没有发生任何化学反应,与电解质有很好的化学相容性。La_1.7Sr_0.3CuO₄电极在700 oC时的极化面电阻为0.16Ω.cm²,这一数值与传统的钙钛矿型ABO₃氧化物阴极材料La1-xSrxCoyFe1-yO₃ （LSCF）十分接近。另外,我们还通过制备La_1.6Sr_0.4NiO₄-CGO及La_1.6Sr_0.4NiO₄-Ag复合阴极,来优化电极的制备工艺,系统研究了考察CGO及Ag的掺杂量对电极电化学性能的影响,选择最优掺杂量来制备出高性能的SOFC复合阴极。结果表明,氧离子导体CGO的加入,使得电极的极化面电阻显著降低,当CGO掺杂量为40 wt.%时,复合阴极的测试极化面电阻值最小,当测试温度为700 oC时,其极化面电阻为0.76Ω.cm²,这一数值为纯La_1.6Sr_0.4NiO₄阴极极化面电阻的四分之一;La_1.6Sr_0.4NiO₄-Ag复合阴极同样表现出良好的电化学性能,当Ag掺杂量为7 wt.%时,复合阴极显示出最佳的电催化活性,700 oC时,其极化面电阻为0.26Ω.cm²,这一数值约为纯La_1.6Sr_0.4NiO₄阴极极化面电阻的十分之一。另外,Ag的加入也改善了电极的阴极极化现象,在相同的电流密度下,电极的极化电位显著下降,,在700 oC测试温度下,当阴极过电位为32 mV时,电流密度达144 mA.cm^-2。总之,本文以寻找一种新型的固体氧化物燃料电池阴极材料为出发点,进行了材料的合成和相关的测试研究,并最终用于中温SOFC的制备中,取得了很好的效果。更多还原

【Abstract】 Solid oxide fuel cells （SOFCs） are a kind of electricity generator with high efficiency and low pollution. The cathode material as SOFC important component is always the priority subject of studies. Strontium doped lanthanum manganate (La_1-xSr_xMnO₃, LSM) is commonly used as ABO₃ type cathode in traditional high temperature solid oxide fuel cells. However, LSM is not suitable to operate in intermediate temperature range, due to the low conductivity and electrochemical activity. For the further improvement of cell performance, the development of high performance cathode material at intermediate temperature is critical. Studies showed that perovskite-like A₂BO₄ type oxide materials exhibited mixed ionic and electronic conducting properties, substantial oxygen permeability, high electrochemical properties, and a relatively high xygen diffusion and surface exchange coefficients.With the ABO₃ type oxides cathode materials for SOFC, A₂BO₄ type oxides generally are lower thermal expansion coefficient （TEC）. The TEC of these oxides match reasonably well with the yttrium stabilized zirconia （YSZ） or Ce_0.9Gd_0.1O_1.9 （CGO） electrolyte materials. Furthermore, A₂BO₄ type oxides show higher electrical conductivity at intermediate temperature, which is extremely advantageouso to the cathode material. All these results imply that A₂BO₄ type oxides are likely to be new cathode materials for （intermediate temperature solid oxide fuel cell） IT-SOFCs. Some preliminary studies on A₂BO₄ type oxides materials in therms of electrochemical properties have been reported. But there are seldom deep researches on electrochemical properties of doping in the A site of the A₂BO₄ type oxide.Cathode materials Ln_2-xSr_xMO₄ （Ln=La, Nd, Sm; M=Ni, Cu） for IT-SOFC were prepared by glycine-nitrate process （GNP）. The chemistry compatibility of the electrode and electrolyte at high temperature and effects of the sintering temperature on the microstructure and electrochemical properties were investigated, respectively. The results showed the sintering temperature has effect on the polarization resistance of the electrode. At moderate temperature, a fine microstructure with moderate porosity and well-necked particles has been formed, and the electrode gave the lowest polarization resistance. Oxygen partial pressure effect experiments have been performed to study the mechanism of the reaction occurred on the electrode. We have studied variations of the electrode polarization resistance with temperatures and oxygen partial pressures, respectively. The results showed that the possible rate limiting step for cathode reaction depends on the oxygen ion transfer process, oxygen adsorption-desorption process and oxygen ion transfer from the TPB to the CGO electrolyte process. The rate limiting step is differect at different temperature and oxygen partial pressure. Sr doped La2CuO4 electrode exhibits fine chemical stability and higher electrochemical catalytic properties. In order to study the chemical stability of electrode with electrolyte materials at high temperature, the sample was prepared by mixing thoroughly La_1.7Sr_0.3CuO₄ with CGO powders, and after heat-treating at 1000 oC for 144 h in air. XRD measyrement, this result indicates that La_1.7Sr_0.3CuO₄ has a good chemical compatibility with the CGO electrolyte. It was found that La_1.7Sr_0.3CuO₄ electrode showed the lowest polarization resistance. That is 0.16Ω.cm² at 700 oC. The polarization resistance of La_1.7Sr_0.3CuO₄ is comparable to that of La1-xSrxCoyFe1-yO₃ （LSCF） Material.La_1.6Sr_0.4NiO₄-CGO and La_1.6Sr_0.4NiO₄-Ag composite electrode were prepared in order to, optimize the electrode preparation technology. Has systematically studied the effect of the CGO or Ag doping amount to electrochemical performance of the composite cathode, and high-performance SOFC composite was prepared cathode by select optimum doping amount. The results showed the addition of oxygen ion conductor CGO notably decreased polarization resistance of the electrode. The addition of 40 wt.% CGO in LSN resulted in the lowest polarization resistance of 0.76Ω.cm² at 700 oC in air, about four times smaller than that of pure LSN cathode. The La_1.6Sr_0.4NiO₄-Ag composite cathode also showed fine electrochemical performance. The addition of 7 wt.% Ag in LSN resulted in the lowest polarization resistance of 0.26Ω.cm² at 700 oC in air, about ten times than that of LSN cathode. Furthermore, LSN-7Ag composite cathode exhibited the lowest overpotential of about 32 mV at a current density of 144 mA.cm^-2 at 700 oC in air. In conclusion, we have explore a new kind of cathode material and we got some nice results when user in on IT-SOFC.更多还原