Abstract
Impedance measurement of Ni/Ni(II) electrode reaction has been made in the LiCl-KCl eutectic melt in the frequency range between 100 K∼0.01 Hz, with regard to the exchange current density, electrical double layer and transfer coefficient. The experiments were made at 500°C under argon atmosphere. The electrode potential of nickel in the molten salt containing NiCl2 (1×10−2∼9×10−1 mol%) revealed a reversible potential. The cathodic polarization curves exhibited a limiting current density controlled by diffusion of nickel (II) ion, whereas the anodic branch obeyed the Tafel relation. The Cole-Cole plot of the electrode impedance consisted of a semicircle at high frequencies and a straight line with a slope of 45° at low frequencies, which corresponded to the charge transfer and diffusion process respectively.The exchange current density obtained from the radius of the semicircle increased with increasing Ni(II) concentration from 1.18 to 9.75×104 A·m−2 the transfer coefficient being 0.49. The double layer capacitance depended strongly on the electrode potential, exhibiting a diffuse-type character.
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