Kinetic study of gallium electrochemical reduction in alkaline solution

Abstract

The article reviews the cathodic process of gallium ion reduction in alkaline solutions. The solution composition influence on the gallium anion reduction kinetics was analyzed by measuring the polarization curves on a dropping mercury electrode. It was found that the cathodic process rate is proportional to the specific adsorption of background cations in the sequence Na+<K+<Li+<Cs+<La3+. A higher rate of reduction of gallium anion present in alkaline solution of lithium cation is a result of participation of the water molecules from the hydration shell of Li+ as a proton donor. In the presence of polyvalent lanthanum cations in alkaline solution, the gallium anion reduction rate increases sharply. This is related to a shift in the ψ1-potential and participation of hydrated cations La(H2O)3+n. The presence of surface-active agents, which have no proton–donor properties, in the solution, complicates the reduction reaction. Certain patterns of the mechanism of the gallium ion discharge reaction in alkaline solutions allow qualifying it as the second group of anions, and the slow stage of the reduction reaction comes down to simultaneous transfer of an electron and proton to the discharging anion. The estimated charge of the discharging gallium anion, which is equal to −0.24 in the transition state of the reaction, is indicative of formation of associates with background electrolyte cations [Me+…GaO2−], [Me+…GaO(OH)2−] by gallate anions in alkaline solutions (рН12).