A novel electrochemical measurement of reversible decomposition potential of sodium chloride at sub-melting temperatures

摘要

The reversible decomposition potential of sodium chloride was measured in the temperature range 419-688 K, using an electrochemical cell Na/beta "-alumina/ NaAlCl4, NaCl, C, Cl-2. In this study, sodium chloride maintained at constant activity levels in the molten electrolyte (NaAlCl4) was electrolysed with a bare minimum electrode polarization to generate gaseous chlorine in-situ, and the reversible back emf of the open cell was measured on current interruption. Alternatively, the cell current could be finely adjusted to make the cell flip over from electrolytic to galvanic cell mode and vice versa to measure the 'zero current potential' without current interruption. These are the first direct measurements of reversible decomposition potential of sodium chloride. The reversible cell potentials are measured here with current interruption on an electrolytic cell, a feat considered difficult due to the non-equilibrium conditions existing in an electrolytic cell for such an ideal measurement. In the temperature range of this study, 688-419 K, the reversible decomposition potential of sodium chloride measured ranged from 3.861 V to 3.597 V. The results are in excellent agreement within 0.05%, with those computed using thermodynamic data reported in the literature, A third-law analysis of the data confirmed that thermodynamic equilibrium conditions existed in the cell during the measurements;This technique may find application in direct measurement of reversible decomposition potential of alkali-metal halides. [References: 4]