Electrosorption of rhodium on a polycrystalline platinum surface has been studied. It has been found that a complete Rh-coverage can be obtained by spontaneous adsorption via the ionization of preadsorbed hydrogen. Underpotential deposition of rhodium has been observed both in 0.5 M H2SO4 and 0.2 M HCl supporting electrolytes. The value of the underpotential shift was found to be about 100-120 mV. (C) 2003 Elsevier Science B.V. All rights reserved.