Ce^(4+)/Ce^(3+)氧化还原体系线性极化与交流阻抗研究

Studies on Ce^(4+)/Ce^(3+)Redox System Using Linear Polarization and Ac Impedance Techniques

用线性极化法和交流阻抗法研究了新型Ce4 + /Ce3 + V2 + /V3 + 氧化还原电池中Ce4 + /Ce3 + 半电池在不同Ce4 +浓度下的电化学行为 .得出Ce4 + 浓度为 0 2mol/L时 ,其极化电阻最小 ,似为理论最佳浓度 .实际应用需综合考虑电池的库仑效率和能量效率等因素 ,还应尽可能选择较高浓度 .测得不同浓度下的阻抗参数表明 ,在Ce(SO4 ) 2 体系处于稳态时 ,不论是慢扫还是使用低的扰动频率 ,Ce4 + 的反应都为传质控制 ;而在体系处于暂态时 ,则不论是快扫还是使用高扰动频率 ,都为传荷控制 ;而当体系介于稳态和暂态之间时 ,则为传质和传荷的混合控制 .因而可通过提高传质速率和加入电化学催化剂的方法来提高Ce4 + /Ce3 + 体系的反应速率 .

The electrochemical behavior of Ce4+/Ce3+ couple with various Ce4+ concentrations in a novel Ce4+/Ce3+-V2+/V3+ redox cell was investigated by linear polarization and ac impedance techniques. The results showed that Ce4+ concentration of 0.2 mol/L seemed to be the optimum concentration, at which the polarization resistance was minimized. But as the Coulomb and energy efficiency was considered in a work cell, the Ce4+ concentration should be selected as high as possible. When the Ce(SO4)(2) system was in a steady state, whether the sweep rate or the disturbance frequency was low, the reaction of Ce4+ was controlled by mass transfer. On the contrary, when the system was in a transient state, whether high sweep rate or high disturbance frequency was used, the reaction was controlled by charge transfer. While if the system was in a state between steady and transient, the whole reaction was controlled by the combination of charge transfer and mass transfer. Therefore, it would be considerably effective for the improvement of Ce4+/Ce3+ reaction to facilitate mass transfer and add electrochemical catalyst.