Citrate is widely used as a complexing agent in electrolytes for deposition of metals and alloys. While the chemistry of metal-citrate complexes is well known, the electrochemical behavior of the citrate ion, particularly on the cathode, was given little attention, although the participation of citrate in the cathodic processes could influence the mechanism of metal deposition and the stability of the plating bath and the properties of the deposits. In the present work, the behavior of Na(3)Cit on Pt cathodes is investigated by the methods of cyclic voltammetry, anodic stripping voltammetry, HR-XPS and ToF-SIMS. Blocking the Pt electrode surface in contact with Na(3)Cit solutions is shown by the methods of stripping voltammetry and HR-XPS, the composition of the blocking film being affected by the electrolysis potential. ToF-SIMS investigations show the presence on the cathode surface of species having a high molecular weight, following electrolysis of the solutions containing sodium citrate. The data obtained allow us to suggest a scenario of formation of a film on the electrode surface. Specific adsorption of citrate anions and catalytic transformation of citrate accompanied by decarboxylation and electron transfer to the electrode surface followed by further reduction of the adsorbed species has been observed. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3560572] All rights reserved.