On the Mechanism of Intermetallic Formation during the Cathodic Co-Reduction of Ions in Molten Salts

—Currently, two mechanisms are known for the electrolytic synthesis of intermetallic compounds (ICs) with simultaneous reduction (co-reduction) of their ions at a cathode in molten salts. Both of them are erroneous. One of them contradicts experimental data and violates the laws of thermodynamics. The other does not represent a co-reduction process, since the ions of both metals rather than one of them should be simultaneously reduced at the cathode. This work does not contain new experimental data and is purely theoretical. A mechanism for the co-reduction process is proposed and thermodynamically justified. We are the first to show that the first IC crystals do not appear on the surface of an electropositive metal: they crystallize on the surface of a binary homogeneous solid solution consisting of the components of the IC having formed at the initial moment of electrolysis. It is shown and thermodynamically confirmed that electronegative metal ions are reduced with depolarization. Electrochemical equations are obtained for the first time for the crystallization of a constant-composition phase during long-term electrolysis and for the crystallization of other intermetallic phases on the surface of the previous ones. The presence of several IC phases in the cathode deposit formed during long-term electrolysis under galvanostatic conditions is explained for the first time. The mechanism of IC electrocrystallization is considered for the cases of galvanostatic and potentiostatic electrolysis modes and for cyclic and square-wave voltammetry. This mechanism is also applicable to the co-reduction of crystallization of metal–nonmetal compounds.