I.V. Zarapina, N.V. Shell, E.Yu. Kopylova, V.I. Vigdorovich

A complex experiment was carried out to study the influence of water content (0,1-50 wt. %) in the mixed solvent C2H4(OH)2 - H2O, hydrogen chloride concentration(0,05-0,99 mol/l) and hydrogenation stimulators on (0.5 - 10 mmol/l) on the kinetics of the hydrogen evolution reaction (HER) on Armco iron and its diffusion through a St3 steel membrane under the corrosion potential of its input side. The nature of the slowed-up stage under the studied conditions is determined by the character of the solvent-s molecules solvating the cathode-s surface. It is principally important that by means of changing the nature and content of the solvent it is possible to purposefully move from the slow discharge to the limiting stage of Hads recombination and the other way round, herewith changing the conditions and level of hydrogen absorption (hydrogenation) of solid phase. In the beginning of water content growth in the mixed solvent, the move is observable from the mechanism of slow discharge to the Volmer-Tafel mechanism with the second limiting stage. The process is controlled by the reaction of recombination at least up to 10 wt. % water inclusive. With water content ~ 80 wt. % on, HER rate is again limited by the Volmer reaction, which determines integral kinetics also in purely aqueous conditions. The presence of arsenic compounds (H3AsO4, H2AsO , HAsO ) only leads to change in the limiting stage in conditionally-anhydrous ethylene-glycol solutions, whereas the insertion of C5H5NH+ ions changes the nature of the slow stage at 2 wt. % H2O. The mechanisms of solid-phase hydrogen diffusion do not depend on the nature of the HER slow stage. Sodium hydro-arsenate and pyridine reveal a stimulating effect over the whole studied interval of concentration. The complete scope of experimental data is satisfactorily interpreted, taking into account the equilibrium disturbance between the over-surface (Hr) and the subsurface (Hs) forms of adsorbed hydrogen, which are responsible for the formation of H2 entering into the gaseous phase and metal absorption leading to its hydrogenous fragility.