Hydrogen insertion in metals: the mechanism and effect of recombination of ad-atoms

The model for hydrogen evolution reaction via a Volmer–Tafel mechanism has been considered, in which a recombination stage was represented as a set of successive and contemporary reactions. The solution of the respective kinetic equation has been obtained for the steady-state regime, which enables us to analyze the balance of the surface processes affecting the metal hydrogenation. It is demonstrated that the diffusing hydrogen flux into the metal bulk is weaker in the case of surfaces with greater concentration of adsorption centres and weaker bond energy between the active centres and hydrogen atoms.