The phenomenon of the sharp decrease of current in the vicinity of the potential of zero charge (pzc) taking place in concentrated solutions is considered in the framework of possible microscopic models of the reaction layer, using a representative system, Pt(II) aquachlorocomplex reduction on mercury, as an example. Polarographic data on the effect of the supporting electrolyte concentration are compared for non-equilibrium and equilibrium bulk solution compositions, and the predominating contribution of the [PtCl3(H2O)](-) complex is concluded from phenomenological analysis. The quantum chemical results are presented for the [PtCl4](2-) anion and the products of its hydrolysis, namely, molecular structures, hydration energies, atomic charge distributions, and the energies of specific adsorption, the latter obtained on the basis of a cluster model. The non-electrostatic reasons for the occurrence of the 'current pit' in concentrated solutions are substantiated.