One to 20 monolayers of Pd were deposited on Pt(1 1 1) and their electrochemical behavior was studied by cyclic voltammetry and impedance spectroscopy. The hydrogen adsorption and absorption is more reversible at deposits on Pt(1 1 1) as compared to Au(1 1 1), probably due to less strain and/or electronic effects. The quantity of hydrogen adsorbed/absorbed at 10 ML are however comparable at both supports. The charge transfer resistance is lower at 1 Pd ML in perchloric and sulfuric acids than for thicker layers, and it is lower at Pd/Pt(111) than at Pd/Au(1 1 1). The adsorption pseuclocapacitance reaches a maximum at 0.214 V in sulfuric acid for 1 ML and there are two peaks at 0.214 V and 0.255 V for thicker layers. Crystal violet increases the reversibility of hydrogen absorption and inhibits hydrogen adsorption although some residual adsorption remains. (C) 2008 Elsevier B.V. All rights reserved.