DISCHARGE OF HYDROGEN-IONS AT METAL CATHODES IN ALKALINE-SOLUTIONS

A survey is given for the measured pH effects in alkaline solutions on hydrogen overpotential. The results are not in accord with the theore tical value for H+ ion discharge, or with that for the discharge of wa ter molecules. This problem arises from neglecting the role of the sto ichiometric number of the reaction in the rate equation. It is suggest ed that H+ ions are discharged, and the adsorbed hydrogen atoms underg o rapid catalytic combination. In this case the stoichiometric number is 2, and the reaction order with respect to H+ ion is 1/2. This mecha nism requires that the overpotential is independent of the alkali conc entration. The mechanism accounts satisfactorily for the slight change s in overpotential with the alkali concentration.