Electrochemical behaviour of LiCl-KCl eutectic melts containing moisture as impurity. Part I: Inert tungsten electrode

Abstract

• Acid-base titration method for estimation of moisture in LiCl-KCl eutectic melts developed. • Redox behaviour of moisture in LiCl-KCl melts at tungsten electrode investigated by EIS. • Suitable equivalent circuit models selected for fitting of complex impedance data. • Contribution of capacitive effects in moisture containing LiCl-KCl melts explored. • Complex impedance data validated by Kramers-Kronig transforms. Voltammetric response of purified LiCl-KCl eutectic melt at 500 ° C is uncomplicated in which cathodic and anodic limits are known to be due to Li + | Li and Cl - | Cl 2 redox couples, respectively. Presence of H 2 O as impurity adds newer characteristics to voltammetric and impedance responses of the melt, as a result of faradaic processes involving formation of OH - and O 2 - in potential region −0.40 to −2.30 V as well as non-faradaic process involving adsorption of OH - at around −1.25 V. Present work was focussed on characterization of moisture containing LiCl-KCl eutectic melts using electrochemical impedance spectroscopy. LiCl-KCl eutectic melts thermally equilibrated with different amounts of H 2 O at 500 ° C were further analysed for residual moisture content by acid-base titration method developed as part of this experimental work. Complex impedance response of different LiCl-KCl eutectic melts at inert tungsten electrode was recorded in potential range −0.50 to −2.50 V to explore contributions of various faradaic and non-faradaic processes due to secondary impurities formed as a result of H 2 O as primary impurity in the melt. Equivalent circuit models were selected to fit complex impedance data of different melts. Validation of impedance data was also performed by Kramers-Kronig transforms in which pseudo- χ 2 values in range 10 - 6 to 10 - 4 were obtained.