The Aluminum Electrode in AlCl[sub 3]-Alkali-Halide Melts

Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl 3 ‐ KCl ‐ NaCl melts between 100° and 160 °C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl 3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and w −1/2 . Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation oyervoltage in AlCl 3 ‐ KCl ‐ NaCl (57.5‐12.5‐20 mole per cent [m/o]) was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/cm 2 at 130°C and a double layer capacity of 40 ± 10 µ F / cm 2 were measured.