Redox behaviour of CaCl2 melts in presence of moisture as impurity. Part II: Electrochemical impedance spectroscopy.

[Display omitted] • Pre-electrolysed CaCl 2 melts investigated at 900 °C in potential range -0.20 to -2.10 V using EIS. • Complex imedance data analyzed by equivalent circuit models at different applied potentials. • CPE and Warburg impedance used for modelling adsorption and mass transport by diffusion. • Effective capacitance at different potentials estimated from CPE data. • Validation of data by Kramers–Kronig transforms; pseudo- χ 2 found in range 10 - 6 to 10 - 4 After exploring in Part I the redox behaviour of CaCl 2 melts at 900 °C in presence of residual moisture impurity and those containing CaCl 2.2H 2 O and Ca(OH) 2 , which resulted in enhancement of effect of moisture in voltammetric features, present work was focussed on extending the experimental work to analyze the impedance response in pre-electrolysed CaCl 2 melt at tungsten electrode in potential range −0.20 to −2.10 V (vs. Ni | NiO as reference) at 900 °C using electrochemical impedance spectroscopy. Two equivalent circuit models were selected for fitting of experimental complex impedance data; one being applicable to potential range −0.20 to −1.60 V and the other one to −1.70 to −2.10 V. Effective capacitance was calculated from values of constant phase element to confirm the strong adsorption effects at specific potentials. Impedance data were also validated by Kramers–Kronig transforms where they showed good compliance fit with pseudo- χ 2 being in range 10 - 6 to 10 - 4 . Impedance response in CaCl 2 melts containing CaCl 2.2H 2 O and Ca(OH) 2 was expected to be similar as mechanism of cathodic reduction of [ (CaOH) 2 2 + ] adsorbed in those melts was exactly same, which was established in Part I of work. [ABSTRACT FROM AUTHOR]