Chemisorption interaction of liquid electrodes of gallium and In–Ga, Cd–Ga and Tl–Ga alloys with solvents in a wide range of their donor numbers

Abstract

By the example of five liquid renewable electrodes of mercury, gallium, and In–Ga (16.4 at.% In), Cd–Ga (0.3 at.% Cd) and Tl–Ga (0.02 at.% Tl) alloys, the structure of electrical double layer (edl) on the sp-metals is studied in several solvents in a wide range of their donor numbers (from 14 to 55). In the solvents with high donor numbers (DN), namely, hexamethyl phosphortriamide (HMPTA, DN = 38.8) and ethylenediamine (EDA, DN = 55), very strong metal–solvent chemisorption interaction was recorded on the Ga, In–Ga, and Cd–Ga electrodes. The energy of chemisorption interaction of the metals with HMPTA and EDA increases in the sequence Hg < Tl–Ga < In–Ga < Cd–Ga < Ga. By the example of HMPTA, it is shown that in the solvents with high DN, the situation is opposite to that observed earlier on these electrodes: strong metal–HMPTA chemisorption interaction does not lead to an increase in the capacitance of edl dense part when passing from the In–Ga electrode to the Ga electrode and, simultaneously, is characterized by a large solvent–chemisorption potential drop. The data for HMPTA and EDA show that the effects of metal–solvent chemisorption interaction for sp-metals are comparable to the similar effects that were observed earlier on the catalytically active metals. This result is the evidence (requiring no additional model concepts) for the correlation between the energy of metal–solvent chemisorption interaction and the DN of solvent. This, in its turn, is a strong proof that specific metal–solvent interaction has a donor–acceptor origin. The results obtained in HMPTA and EDA enable us to generalize the available data for the structure of edl on the catalytically active and sp-metals.