FORMATION OF CRYSTALLINE INTERMETALLIC COMPOUNDS AND SOLID-SOLUTIONS IN ELECTROCHEMICAL INCORPORATION OF METALS INTO CATHODES

The elementary act of cathodic incorporation of metal into metal is an electrochemical transition of a metal ion from solution (or melt) into the cathode with formation of a solid chemical compound between the two metals. Unlike chemisorption the elementary act of incorporation occurs not only at interface but also inside the solid metal phase and depends strongly on its crystalline structure. Electron transfer in incorporation is always complete (not partial). It follows from nonequilibrium thermodynamics that when the incorporation rate is limited by crystallization of an intermetallic layer, it is linearly related to potential within the homogeneity region of intermetallic compounds. If the rate is limited by incorporated metal diffusion in the intermetallic compound, the square of the rate is linearly related to potential. Incorporated metal can react chemically with a solution component, reducing it. If the rate of this reaction is less than that of incorporation and not limited by oxidant diffusion in solution, in the cases investigated (solid intermetallic compounds of alkali metals) the chemical reaction rate is linearly related to potential. This follows from the activated complex theory. The equilibrium potentials of intermetallic compounds formed in incorporation are more positive than those of single metals being incorporated (sometimes by 1.5 V). The electrochemical incorporation of metals has numerous applications. © 1979.