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The parameters of the H2 evolution reaction on Pt have been determined as a function of current density (c.d.) pH, salt addition, mode of electrode preparation, aging and degree of preelectrolysis; and as a function of c.d., and degree of preelectrolysis for W and Ag. On Pt, Tafel slopes (b) and exchange currents (if) varied with mode of preparation, that in air giving a slope of 2.303 RT/F compared with the more usually observed slope of 2.303 RT/2F; anodic activation gives high and reproducible ¿o's. Aging decreases i0 and extends the c.d. range in which b = 2.303 RT/F. Successive increase of preelectrolysis causes it, to increase to a limiting value. Anodic activation occurs only at a c.d. > 10 "2 amp. cm. ~2 and is independent of the amount of current passed and subsequent reduction. The stoichiometric number (v) is unity. On W and Ag Tafel lines had two distinct slopes; v = 1 in 0.1-0.4 N solution. There is no intrinsic screening effect due to a Luggin capillary. Previous work on Pt in pure solutions indicating b > 2.303 RT/F is reinterpreted in terms of partial diffusion control. Anodic activation on Pt is due to both mechanical cleaning and oxidation. The limiting c.d. for activation is that at which H2 depolarization is negligible. Tafel slopes of RT/F are consistent with migration of H atoms over the surface as rate determining. Calculation of the rate of change of the potential of the layer of ions in contact with the electrode with that of the electrode indicates that near the electrocapillary maximum Tafel slopes may be changed to lower values.slopes occur in pure solutions depending on current density.3(1) .

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The adsorption of thiourea on iron cathodes has been studied in 0.1 N sulphuric acid solution containing 10−1 and 10−2 Mol of thiourea at 30, 40 and 50 °C. The surface coverage has been calculated by comparing current density (at constant potential and temperature) of solutions with and without inhibitor. The results show that adsorption is due to specific adsorption forces of molecules and HS− anions as well as to electrostatic forces of cations. The authors have determined the adsorption energy and the enthalpy, free standard energy and entropy of adsorption. On the basis of these results it is feasible to presume that thiourea would be rather efficient an inhibitor of the corrosion for iron acid solution.

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