The aim of this research is to study the interface gold/perchloric acid solution in presence of hydrogen. The reactive is generated by H(+) ion reduction and by saturating the electrolyte with the gaseous H(2). No evidence of H(2) dissociative adsorption is found. In special conditions, a strongly adsorbed layer is formed from the atoms diffusing from inside of the metal. The mass transport occurs in three ways: the diffusion of H atoms inwards, the diffusion of H atoms back to the surface and the dissolved H(2) diffusion from the bulk electrolyte to the surface. When dissolved H(2) reacts, the reaction is kinetically controlled when the H(2) partial pressure is high, and it is diffusionally controlled when the reactive partial pressure is low. Above 0.7 V, (measured vs. RHE), the (100) plane surface reconstruction lifts, and the rate determining step is the H diffusion towards inside of the metal, and the current suddenly falls. The Hydrogen redox reaction on gold shows reversibility with respect to the potential when the reactives are the H diffusing outwards of the metal and the H(+) ion present in the electrolyte. However, the absolute current values of oxidation and reduction are different because the reactive sources are different. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.