Under rigorously controlled conditions in dimethylformamide containing a tetramethylammonium salt (TMABF(4), TMAClO(4), TMAI), platinized platinum layers exhibit a reversible charging process that occurs at quite negative potentials (more negative than -2.2V vs. SCE). The mode of insertion of the electrolyte and the reversibility of the platinum charging are discussed according to the nature of the salt. The stoichiometry of this ionometallic layer, formed after its total saturation with ions, has been estimated with the aid of coulometry and microbalance (EQCM) measurements. After several charge-discharge processes, the platinized layer is progressively transformed into a smooth platinum surface. A mechanism is proposed to explain this annealing phenomenon, which is linked to reduction-oxidation cycles. (c) 2006 Elsevier B.V. All rights reserved.