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 theoretical value for H+ ion discharge, or with that for the discharge of water molecules. This problem arises from neglecting the role of the stoichiometric number of the reaction in the rate equation. It is suggested that H+ ions are discharged, and the adsorbed hydrogen atoms undergo rapid catalytic combination. In this case the stoichiometric number is 2, and the reaction order with respect to H+ ion is 1/2. This mechanism requires that the overpotential is independent of the alkali concentration. The mechanism accounts satisfactorily for the slight changes in overpotential with the alkali concentration.