Potentials of zero total and zero free charge of platinum group metals

Abstract Some fundamental definitions and relations of the thermodynamic theory of the platinum electrode are considered. The notions of the potential of zero total charge (pztc) of the first and second kind are discussed. It is shown that in the presence of excess of surface-inactive ions, the potential of zero total charge of the second kind can be regarded as the potential of zero free charge (pzfc). The pzfc is an analogue of the pzc of metals not adsorbing hydrogen and oxygen. The methods of determination of the pztc and the pzfc of platinum metals, of their dependence on solution pH and salt concentration are considered, as well as the dependence of the pzfc on surface coverage with adsorbed hydrogen. Tables listing the pztc and the pzfc of platinum metals are given. The conditional nature of the notions pzfc and the charge of the double layer in the presence of strong chemisorption of ions is demonstrated and the difference between the formal and the true coefficients of charge transfer is emphasized. The notion of the charging curves and electrocapillary curves of the first and second kind is introduced and the methods of their finding are discussed. The electrocapillary curves of the first and second kind are given for platinum in solutions of different composition.