The reversibility of metal platinum electrode interfaced with heteropolycompound (HPC) in hydrogen-argon and hydrogen-air environments is investigated. The kinetic of relaxation and potential equilibration of this interface after hydrogen concentration change is studied. The concentration dependencies of pure thermodynamic potential (in argon) and of the equilibrium potential (in oxygen) are measured. There is a correlation between the nature of anion and cation of HPC and chemical reaction or adsorption control of relaxation. (C) 2003 Elsevier B.V. All rights reserved.