The electrochemical behavior of Ce~(4+)/Ce~(3+) couple with various Ce~(4+) concentrations in a novel Ce~(4+)/Ce~(3+)-V~(2+)/V~(3+) redox cell was investigated by linear polarization and ac impedance techniques. The results showed that Ce~(4+) 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 Ce~(4+) concentration should be selected as high as possible. When the Ce(SO_4)_2 system was in a steady state, whether the sweep rate or the disturbance frequency was low, the reaction of Ce~(4+) 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 Ce~(4+)/Ce~(3+) reaction to facilitate mass transfer and add electrochemical catalyst.

Key words: POLARIZATION, IMPEDANCE, CERIUM COMPOUNDS, ELECTRO-CATALYSIS, REACTION RATE