LiCl-KCl-LaCl_(3)熔盐体系中La^(3+)的反应动力学机理

Kinetic Mechanism of La^(3+) Reaction in LiCl-KCl-LaCl_(3) Molten Salt System

在LiCl-KCl共晶盐中,研究了在不同温度下La^(3+)的反应动力学机理。首先,在723~873 K范围内,利用循环伏安法(CV)测得La^(3+)的扩散系数D为3.06×10^(-5)~6.08×10^(-5)cm^(2)/s,并根据Arrhenius方程计算了La^(3+)在电解质中的扩散活化能E_(D)=34.51 kJ/mol。随后,利用电化学阻抗谱技术(EIS)研究了La^(3+)在电极上的动力学参数并测得交换电流密度i_(0)为0.48~1.39 A/cm^(2)、反应速率常数k_(0)=2.04×10^(-4)~5.90×10^(-4)cm/s及反应活化能E_(a)=35.04 kJ/mol。通过Nyquist图和拟合的等效电路图研究La^(3+)在W电极上的反应动力学机理,发现在LiCl-KCl共晶盐中La^(3+)的电化学反应速率不仅受扩散控制还受电荷转移控制,且与温度成正相关。

In this paper,the reaction kinetic mechanism of La^(3+) was studied in the LiCl-KCl eutectic salt at various temperatures.First,the diffusion coefficient of La^(3+)(D)measured by cyclic voltammetry(CV)increases from 3.06×10^(-5) cm^(2)/s to 6.08×10^(-5) cm^(2)/s with the temperature ranging from 723 K to 873 K,and the activation energy of La^(3+) diffusion(E_(D))in the molten salts is 34.51 kJ/mol calculated by the Arrhenius equation.Subsequently,the kinetic parameters of La^(3+) on the W electrode were studied by the electrochemical impedance spectroscopy(EIS).In the temperature range of 723-873 K,the exchange current density(i_(0))is measured to be 0.48-1.39 A/cm^(2),and the reaction rate constant(k_(0))is determined as 2.04×10^(-4)-5.90×10^(-4)cm/s.Moreover,the corresponding reaction activation energy(E_(a))is found to be 35.04 kJ/mol.The Nyquist plots and the fitted circuit diagrams explored the reaction kinetic mechanism of La^(3+) on a W electrode.It was illustrated that the electrochemical reduction rate of La^(3+) in the LiCl-KCl eutectic salt is controlled by diffusion and charge transfer,and it is positively correlated with temperature.