Sm0.5Sr0.5CoO3阴极氧还原动力学

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.

Kinetics of Oxygen Reduction over Sm0.5Sro.5CoO3 Cathode

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 (pO2), 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 pO2 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.