Hydrogen sorption at Pd films of 20-80 nm deposited oil a polycrystalline gold electrode was studied in sulfuric and perchloric acid. Assuming that the hydrogen adsorption does not vary with the Pd films thickness, hydrogen adsorption/absorption charges in Pd were separated in the two contributions in the hydrogen-poor alpha-Pd-H phase. The results are compared to those obtained at Pd monolayers on Au(1 1 1). The adsorption on polycrystalline Pd begins at potentials more negative than on 0.8 ML Pd on Au(1 1 1) and is not much affected by the nature of anion (sulphate or perchlorate). contrary to the thin layers on Au(1 1 1). The absorption charge in alpha-PdH phase in the potential range of 0.08-0.15 V was found to be similar to that at a 25 mu m Pd foil in this potential range while at more positive potentials it is larger. In the presence of crystal violet which adsorbs at the electrode surface it was found that some residual H adsorption exists. There is more hydrogen absorbed in Pd in the presence of crystal violet in the hydrogen-poor alpha phase but in the hydrogen-rich beta phase the amount of hydrogen is the same. (c) 2007 Elsevier Ltd. All rights reserved.