The relation between the potential of zero charge and work function for sp-metals

Abstract

It is shown that for numerous sp-metals there exists no unified work function (We) dependence of the potential of zero charge Eq = 0 and the potential drop characterizing the metal lyophilic behavior ΔMHgEchem)q = 0. The reason is that the metal work function is by no means the only factor affecting the value of Eq = 0. The quantities Eq = 0 and (ΔMHgEchem)q = 0 depend also on the distance of the solvent dipoles’ closest approach to metal surfaces (dms) in the absence of the metal-solvent chemisorption interaction. When the metal-solvent chemisorption interaction is involved, this distance affects the degree of overlapping of the metal’s acceptor levels and the upper occupied donor levels in the solvent molecules. To reliably investigate the effect of any of these factors on Eq = 0, the other one should be fixed up. It is shown, by example of Ga-, Bi-Gaand Sn-Ga-electrodes, as well as Pb-Ga-, In-Ga-, and Cd-Ga-electrodes demonstrating very close values of the “electrochemical work function” that the metal-solvent chemisorption interaction becomes stronger with the decreasing of dms. The influence of this factor is intensified with the increasing of the solvent’s donor number DN. The We dependence of Eq = 0 and (ΔMHgEchem)q = 0 can be traced by example of metals with nearly equal dms values, e.g., Tl-Ga, In-Ga, and Ga. In all studied solvents, the deviation of Eq = 0 from We increased in the series Tl-Ga < In-Ga < Ga, that is, with the increasing of the metal’s work function in vacuum. The effect is intensified with the increasing of the solvent’s DN. The obtained results agree with the concept of donor-acceptor nature of the metal-solvent chemisorption interaction.