Mechanism of Hydrogen Evolution at Tellurium in Hydrochloric Acid Cathodes

Hydrogen overpotential ttellurium cathodes was studied in the concentration range 0.005N-5N aqueous hydrochloric acid at 30 ~ The results indicated absence of specific adsorption. In dilute solutions a simple electrochemical mechanism, with two Tafel line slopes of 0.04 v and 0.12 v at 30 ~ was established as the rate-determining mechanism. In concentrated solutions, a rate-determining dual electrochemical catalytic mecha-nism, with a slope of 0.06 v at 30 ~ was uggested to explain the results in the low cur-rent density range. This dual mechanism changed to a simple one at high cathodic polarization. Theoretical calculations of the Tafel line slopes for various dual mechanisms were also carried out. It was found that, for a dual slow discharge lec%roehemical mechanism or a dual slow discharge catalytic mechanism, the slope was exactly the same as that for the simple slow discharge, i.e., 0.12 v at 30~ The effect of neutral salts on hydrogen overpotential, ~ at constant pH was studied. Addition of lanthanum chloride increased the numerical value of ~ at constant pH and current density. From the salt effect on ~ in 0.05N hydrochloric acid, the zeta potential was calculated and was found to have a value of ca. 0.05 v