Electrochemical analysis of trace amounts of water in propylene carbonate electrolytes

Abstract

Cyclic voltammetry and limiting currents to an rde have been used for the determination of the water in the 0.3–20 ppm range, in PC electrolytes. Carefully dried solutions yielded voltammetric peaks proportional to the amount of water added. In KPF 6 electrolytes, the cathodic current corresponding to the reduction of water was at 0.48 V, while in KAlCl 4 solutions the reduction occurred already starting at 2.8 V, both relative to a K/K + reference. At these potentials, the current to an rde showed Levich type dependence on rpm and was proportional to the concentration of water in the range 0.5–20 ppm. The calculated diffusion coefficients of water are higher than expected: 25°C, D H 2O = 8.5±2 × 10 −6 cm 2 s −1 in 0.5 M KPF 6, while in 0.25 M KAlCl 4 D H 2O , 10±2 × 10 −6 cm 2 s −1.