Electrochemical Impedance Spectroscopy Studies of Corrosion of Two-phase Ni-Dy Alloys in Molten (0.62Li,0.38K)2CO3 at 650 °C

Abstract

AbstractThe dissolution of the NiO cathodes and the corrosion of bipolar plates are great obstacles to the commercialization of molten carbonate fuel cells (MCFC). Rare earth element dysprosium is effective in inhibiting the corrosion of Ni in molten carbonates. In this presentation, electrochemical impedance spectroscopy was employed to study the corrosion behavior of two-phase Ni-Dy alloys containing 1 and 3 wt.% Dy, respectively, in molten (0.62Li,0.38K)2CO3 at 650 °C in air. The experimental results indicate that the Nyquist plots for the corrosion of both Ni-1Dy and Ni-3Dy are all composed of a small capacitive loop at high frequencies and a line at low frequencies, but with larger impedance values for Ni-3Dy. The emergence of Warburg impedance at low frequencies suggests that the corrosion of alloys is controlled by the diffusion of oxidants in molten carbonates, as observed for pure nickel. The addition of dysprosium to nickel can decrease its corrosion rate, with a better effectiveness for the 3% Dy addition. Based on the diffusion impedance, the oxidants involved in corrosion are also discussed.