Ammonium hexachloroplatinate (IV) ((NH4)(2)PtCl6) has been shown to be a good precursor to obtain metallic Pt by thermal decomposition, in addition to being a stable compound easily obtained from a variety of Pt recovery processes, such as fuel cell electrode recycling. Its low decomposition temperature and its relatively high water solubility make it a suitable choice to produce Pt on carbon for proton exchange membrane (PEM) fuel cells, however, it has not been found reported as precursor in the preparation of Pt/C for PEMFC. This work presents the characterization of Pt/C catalysts prepared with a new method employing both commercial and synthesized (NH4)(2)PtCl6 as well as commercial Pt(NH3)(4)Cl-2 for comparison. With this method, the production of Pt/C using Pt(NH3)4Cl(2) yields lower loadings than with (NH4)(2)ptCl(6). It is proposed that supporting Pt/C using (NH4)(2)PtCl6, takes place by adsorption on the carbon surface of the ptC(6)(2-) and the 16 Pt(II)Cl-3(-) when it is reduced from Pt(IV). Not only were oxygen complexes at the carbon surface found to have an effect on Pt loading and on the Pt particle size distribution of the samples prepared but also on the in situ Pt reduction-carbon oxidation during the reaction. (C) 2004 Elsevier B.V. All rights reserved.