Electrochemical investigation of NaOH-Na2O-Na2O2-H2O-NaH melt by EMF measurements and cyclic voltammetry

Abstract

Thermodynamic activity of sodium oxide and oxidation potential in NaOH-Na2O-Na2O2-H2O- NaH melt at the temperature of 400°C was investigated. Galvanic cell for the potentiometric measurements consisted either of a sodium electrode formed by β and βʺ-alumina semi-closed tube filled with liquid sodium or a platinum wire and of an oxygen electrode made from ZrO2 (Y2O3) solid electrolyte with the Bi-Bi2O3 reference mixture. The number of exchanged electrons determined from the electromotive force measurements was in good agreement with the assumed reactions. The activity coefficient of sodium oxide was lower than one. Voltammetric measurements were carried out with a sodium reference electrode and a nickel auxiliary electrode. Behaviour of platinum, gold, silver and nickel as working electrodes was studied. The experiments were carried out in nitrogen atmosphere. Several types of zirconia semi-closed tubes were tested for long-term measurements under the process conditions.