Pt-based electrocatalysts can be prepared by spontaneous deposition at the open-circuit potential. With this method, Pt was successfully deposited on Ti upon immersing freshly polished Ti samples in an aqueous solution of 0.1 M HClO₄ containing K₂PtCl₆. In subsequent studies, the method has further been developed in a two-step procedure. Thus, Pt and Au-based catalysts have been prepared by electrochemical deposition of M particles (M = Cu, Pb, Ni, Co) onto carbon supports (first step), which had their surface layers replaced by Pt or Au (second step). The replacement has been achieved by a spontaneous partial exchange of the non-precious metal deposits with Pt or Au upon their immersion in aqueous acid solutions containing chloroplatinate and/or chlorolaurate anions. Electrochemical and sputter-etch AES characterization has shown that the bimetallic Pt/M and Au/M catalysts consist of Pt or Au shell and a well mixed Pt-M and Au-M core. This preparation route is of both fundamental and practical interest. First, it allows the study of the electronic effect of the second metal present in the particle core on the pure Pt or Au catalyst skin. At the same time, if an inexpensive metal M is deposited on high surface area carbons (of fuel cell type) and then its surface layer is effectively replaced by Pt or Au, the methods could lower the amount of precious metal used. The resultant Pt(M)/C and Au(M)/C electrodes were tested for their catalytic activity  in electrochemical reactions of technological interest, such as the hydrogen evolution, oxygen reduction, methanol oxidation and borohydride oxidation.