Decomposition voltage for the electrolysis of alumina at low temperatures

The apparent decomposition voltage for the electrolysis of alumina in an equimolar Na₃AlF₆-Li₃AlF₆ electrolyte was measured over a temperature range of 800 to 1000° C by the extrapolation of voltagecurrent plots to zero current. Temperature coefficients of –1.9 and –2.4 mV° C^–1 were determined for conditions of variable alumina activity (constant concentration) and unit activity (saturated), respectively. The overvoltage contribution to the temperature dependency was estimated to be about –1.6mV° C^–1 (versus a –0.6 mV° C^–1 dependency for the reversible decomposition voltage). Reduced alumina solubility at low temperatures also appeared to increase the overvoltage, but was of secondary importance.Based on work partially supported by the US Department of Energy (Contract DE-AC03-76CS40215: Energy Savings Through the Use of an Improved Reduction Cell Cathode).