Abstract: The main objective of developing molten salt electrolysis refining technology is to achieve the effective separation of Ln/An elements. The examination of the electrochemical behavior of lanthanides, with a particular focus on La³⁺ during electrolytic refining, provides valuable insights into the impact of accumulated cationic fission products, notably Cs⁺, on the electrochemical dynamics within a LiCl-KCl molten salt matrix. This investigation employed a comprehensive approach, utilizing advanced simulation techniques alongside experimental methodologies such as cyclic voltammetry, chronoamperometry, linear polarization, and electrochemical impedance spectroscopy, to elucidate the intricate interactions at play in this electrochemical environment. Preliminary evaluations of the electrochemical properties of La³⁺ ions were conducted on both tungsten(W) and liquid gallium(Ga) electrodes using cyclic voltammetry. The results reveal a notable shift in the reduction potential of La³⁺ towards more negative values as the concentration of Cs⁺ increases. This behavior can be ascribed to competitive ion interactions and modifications in the electrochemical milieu, which impede the reduction efficiency of La³⁺ ions. Subsequent experiments employing chronoamperometry were utilized to elucidate the diffusion behavior of La³⁺ ions within the molten salt matrix. The results demonstrate a marked decrease in the diffusion coefficient from 1.08×10⁻⁵ cm²/s to 4.80×10⁻⁶ cm²/s as Cs⁺ concentration escalated. This decline suggests a notable impediment to ion mobility, likely due to the increased viscosity and ion crowding within the electrolyte as Cs⁺ accumulates. Further kinetic analyses of the La³⁺ reduction on liquid Ga cathode were conducted utilizing linear polarization and electrochemical impedance spectroscopy. The investigation reveales a substantial decrease in the exchange current density(i₀) from 0.302 A/cm² to 0.084 5 A/cm² with increasing Cs⁺ concentrations, indicating a marked deceleration in the kinetics of the reduction reaction. Concurrently, the activation energy(E_a) for the reduction process increases from 26.77 kJ/mol to 39.24 kJ/mol, suggesting a heightened energetic barrier for the electrochemical transformation. In addition, equivalent circuit modeling of the alternating current impedance spectra indicates that the physical properties of the electrolyte are significantly altered by elevated Cs⁺ levels. Notably, an increase in solution resistance is observed, further supporting the conclusion that Cs⁺ presence considerably modifies the electrolyte characteristics, thus impacting the overall electrochemical behavior of lanthanides during refining processes. In summary, the accumulation of cationic fission products, particularly Cs⁺, within a LiCl-KCl molten salt matrix profoundly influences the electrochemical properties and reaction kinetics associated with lanthanide reduction. This finding underscores the critical importance of thoroughly assessing these interactions to inform the design, optimization, and overall efficacy of electrolytic refining techniques employed in the separation and recovery of valuable lanthanides.