A thermodynamic description of the Peltier heat at the aluminum and the oxygen electrode in the system NaF±AlF 3 ±Al 2 O 3 is given. The thermoelectric power in melts with molar ratios n NaF an AlF 3 from 3.0 to 1.0, saturated with alumina are measured. Seebeck coef®cients for molten¯uoride electrolytes saturated with alumina, electrolytes that are relevant for aluminum electrowinning electrolysis cells, are reported. The results allow determinations of Peltier heats of aluminum, oxygen and

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... on electrodes in NaF±AlF 3 electrolytes saturated with alumina. For molar ratios of n NaF an AlF 3 between 2.6 and 1.2, there is a Peltier heating of the aluminum cathode. This heating is in the same order of magnitude as the electrolyte Joule heat, when the current density is 0.7 A cm À2 . For molar ratio n NaF an AlF 3 equal to 1.0 the Peltier effect at the aluminum electrode approaches zero. From theoretical considerations we expect a drop also for molar ratio 3.0. For the anode we report a Peltier cooling that is larger than the heat produced by the anodic overvoltage, in melts with NaF/AlF 3 molar ratio between 2.6 and 1.2 saturated with alumina. 126 B. E. Flem et al.