Sm_(0.5)Sr_(0.5)CoO_3阴极氧还原动力学

Kinetics of Oxygen Reduction over Sm_(0.5)Sr_(0.5)CoO_3 Cathode

利用极化、交流阻抗技术考察了担载于La0.9Sr0.1Ga0.8Mg0.2O3(LSGM)电解质上的Sm0.5Sr0.5CoO3-La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(SSC-LSGMC5)复合阴极的氧还原反应动力学.在SSC-LSGMC5阴极氧还原反应的阻抗谱中可以观察到明显的两个半圆.高频环的电导与氧分压无关,低频环的电导正比于氧分压的0.5次方.并且低频环的氧分压级数随着反应温度的降低而减小,可能对应于吸附氧原子的扩散过程.SSC-LSGMC5极化曲线与经典的Butler-Volmer方程吻合.阴、阳极的电荷转移系数均为1左右,交换电流密度的氧分压级数为1/4,对应于电荷转移过程.实验结果显示SSC-LSGMC5上的氧还原反应机制随反应条件的不同而发生变化.

The kinetics of oxygen reduction over Sm0.5Sr0.5CoO3 La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(SSC LSGMC5) cathode was investigated using polarization and AC(alternating current) impedance. Two arcs were observed in the impedance spectra of SSC LSGMC5 at near equilibrium conditions. The conductivities of the high frequency arcs had no dependency on oxygen partial pressures (), and showed an activation energy about (1.0～ 1.1)× 102 kJ· mol- 1. The dependency of the conductivities of the low frequency arcs decreased from 0.6 to 0.4 with the decrease in temperature 1073～ 873 K, accordingly,the activation energies increased from 1.3× 102 to 1.6× 102 kJ· mol- 1 with the increase in (2× 104～ 1× 105 Pa). The high frequency arcs could be related to the transfer of oxygen ions across the electrode/electrolyte interface, while the low frequency arcs could correspond to the diffusion of oxygen atoms from the electrode surface to the three phase boundary. The polarization curves of SSC LSGMC5 agreed well with the Butler Volmer equation. The anodic and cathodic charge transfer coefficients were all about 1 and the dependency of the exchange current density was around 0.25, suggesting a rate determining step of charge transfer. The mechanism of oxygen reduction over SSC LSGMC5 depended strongly on the over potential and reaction temperature.