电导弛豫法研究SOFC阴极材料

1、利用电导弛豫方法研究燃料电池阴极材料利用电导弛豫方法研究燃料电池阴极材料小组小组成员成员：谢云，史鼐，孙乐，陈明龙，黄晋，马致远。报告人报告人：史鼐Outline:SOFC背景介绍应用举例电导弛豫方法及影响因素总结O-SOFC示意图示意图P-SOFC示意图示意图燃料电池阴极反应燃料电池阴极反应La0.6Sr0.4Co0.2Fe0.8O3-d表面氧交换表面氧交换 k(cm s-1)内部氧扩散内部氧扩散 D(cm2s-1)传统测量方法：两端子法（伏安法）传统测量方法：两端子法（伏安法）四端子法测电导率四端子法测电导率接触点和导线电阻不可接触点和导线电阻不可忽略，尤其对电阻较小的材料，测量不准确忽略

2、，尤其对电阻较小的材料，测量不准确四端子法测量电导率四端子法测量电导率四端子法测电阻示意图四端子法测电阻示意图Fick第二定律：22CCDtx0( ,0)C xC00 xCx (, )xlCDk Cl tCxECR理论基础理论基础其中其中l为最小心样品尺寸的一半为最小心样品尺寸的一半定义复合函数定义复合函数,( )T(t)F x tC x tCX x（） （）22FFDtx边界条件为：边界条件为：0( ,0)F xCC00 xFx(, )xlFDkFl tx通过分离变量，可得：XTXDT 0XX(0)0X( )( )DX lkX l0TD T（1）（2）边界条件：讨论取值只有当0时满足，解得代

3、入边界条件可得 20C tanklD 12cossinXCxCx 令令l tanlkD 有有最后代入函数并化简得最后代入函数并化简得20n214(C -C )sinC(x,t)-Ccosexp()sin2nnnnnDxtll 。（1） 即 时，若令 ，则 ，可得 （1） 即 时，若令 ，则 ，可得 0lkD/lD k/clD kcllt00C -C1 exp()C -Cktl 根据质量守恒及缺陷平衡方程可得则 此时材料电导率仅与时间t有关，与 样品内位置x无关，可认为样品电导率均匀分布( )(0)( )(0)( )(0)( )(0)toohhoohhMC tCC tCtMCCCC )1 exp

4、()tktl 表面扩散控制表面扩散控制（2） 即 时， lkD cll2t020C -C)81exp()C -C4tDtl （3） 时， tannnlkD cll22t0n2210C -C4sin1exp()C -Csin2nnnnnDtl 体扩散控制体扩散控制双重控制双重控制理论基础推广到三维，归一化电导弛豫曲线：其中：弛豫曲线与氧分压关系弛豫曲线与氧分压关系理论基础拟合求解拟合求解方法一：方法一：1, 确定确定D,k初步范围初步范围2, 求解误差分布求解误差分布3, 筛选结果筛选结果(控制步骤）控制步骤）方法二：1, 选定初始D,k值2, 拟合优化D,k结果3, 变换初始值多次拟合SFM样

5、品弛豫曲线的拟合误差与D、k值的关系Relative asymptotic errors on the estimated k and D获得获得D,k值的影响因素值的影响因素拟合影响拟合影响Francesco Ciucci, Solid State Ionics 239 (2013) 2840获得获得D,k值的影响因素值的影响因素气体切换速度气体切换速度时间时间常数常数M. W. den Otter, H. J. M. Bouwmeester, B. A. Boukamp, H. Verweij, Journal of The Electrochemical Society, 148 (20

6、01) J1-J6获得获得D,k值的影响因素值的影响因素氧分压梯度氧分压梯度对于对于LSCFS. Wang, A. Verma, Y.L. Yang, A.J. Jacobson), Ben Abeles, Solid State Ionics 140 (2001) 125133获得获得D,k值的影响因素值的影响因素表面微观结构表面微观结构晶粒大小晶粒大小晶界晶界密度（长度）密度（长度）原料分体性质原料分体性质烧结温度，时间烧结温度，时间制备过程制备过程Yunlong Wang, Yao Wang, Changrong Xia, Journal of The Electrochemical S

7、ociety, 159 (9) F570-F576 (2012) ECR应用举例应用举例Sr3YCo4O10.5电极材料电极材料Preparation method: SSR (SrCO3, Co3O4, Y2O3)Sintering temperature :9001200Sample sintering temperature: 1180/4hDensity 95%Size: t=1.43mm, w=1.09mm,l=19.72mmElectrical conductivity of Sr3YCo4O10.5 in airMax=550S/cmOxygen vacancies format

8、ionThermal activationA relative electrical conductivity vs. time profile obtained during an ECR experiment at 850 with an oxygen partial pressure switch from 10% to 75% and the corresponding fit Comparing of profiles of relative conductivity. g(t).of Sr3YCo4O10.5 vs. time obtained during ECR experim

9、ents at different temperatures and for switches of oxygen partial pressure from 10% to 75%ECR应用举例应用举例Sr3YCo4O10.5电极材料K和初始氧分压无关，和初始氧分压无关，和平衡氧分压有关和平衡氧分压有关D和氧分压无关，只和和氧分压无关，只和温度有关温度有关Arrhenius plot of the chemical oxygen diffusion and chemical surface exchange coefficients obtained for Sr3YCo4O10.5 by E

10、CR experimentsECR应用举例应用举例Sr3YCo4O10.5电极材料Dependence of chemical surface exchange rate for Sr3YCo4O10.5 on the final oxygen partial pressure during ECR switchesOxygen content in Sr3YCo4O10.5 dependence on oxygen partial pressure in the surrendings and temperature determined by TGA温度升高，氧浓度减少温度升高，氧浓度减少

11、ECR应用举例应用举例Sr3YCo4O10.5电极材料热力学热力学因子因子自扩散自扩散系数系数Comparison of oxygen self-diffusion coefficients in Sr3YCo4O10.5 determined by ECR(this work),IEDP/SIMS and molecular dynamicsECR应用举例应用举例Sr3YCo4O10.5电极材料ECR应用实例应用实例水对电极材料的影响水对电极材料的影响Schematic representation of cathode reaction in protonic ceramic fuel c

12、ells(PCFCs)Ho-Il Ji, Sung-Min Choi, Kyung Joong Yoon, Ji-Won Son, Byung-Kook Kim, Hae-Weon Lee, Jong-Ho Lee, Solid State Ionics 249250 (2013) 112116Variations in conductivity after the gas was changed from dry air to wet air at 700. Conductivity relaxation curve during a cycle of changes in the gas

13、from wet to dry air and then from dry to wet air in (b) region(i)and region (ii).abcECR应用实例应用实例水对电极材料的影响水对电极材料的影响Conductivity change after the gas was changed from dry air to wet air. Conductivity relaxations upon oxygen reduction in (b) region (i) and region (iii).ECR应用实例应用实例水对电极材料的影响水对电极材料的影响XPS d

14、epth profiling analysis on LSCF cathode after long-term exposure(150h) in wet atmosphere.ECR应用实例应用实例水对电极材料的影响水对电极材料的影响ECR应用实例应用实例水对电极材料的影响水对电极材料的影响ECR应用实例应用实例元素中毒对电极的影响元素中毒对电极的影响Ling Zhao, Tatsumi Ishihara and San Ping Jiang, Journal of The Electrochemical Society, 160 (6) F682-F686 (2013)SEM microg

15、raphs of LSCF surface after heat-treatment for 48 h in the absence of E-glass at (a) 700 C, (c) 750 C, (e) 800 C and in the presence of E-glass at (b) 700 C, (d) 750 C, (f) 800 C.(g) Without heat treatmentECR应用实例应用实例元素中毒对电极的影响元素中毒对电极的影响SIMS depth profiles analysis of LSCF surface after heat-treatmen

16、t in the presence of E-glass for 48 h at (a) 700 C, (b) 750 C and (c) 800 C.ECR应用实例应用实例元素中毒对电极的影响元素中毒对电极的影响Experimental data of electrical conductivity relaxation as a function of time on LSCF in the presence of E-glass at 700,750,800 C测试测试-降温降温升温（升温（5/min）-测试测试ECR应用实例应用实例元素中毒对电极的影响元素中毒对电极的影响Plots of fitted surface exchange coefficients as a function of time in the absence and presence of E-glassECR应用实例应用实例元素中毒对电极的影响元素中毒对电极的影响总结总结ECR测试方法相比于其他测试方法操作更加简便，所需设备更加简单，耗时更短。测试方法