Over-Potential of the Hydrogen Isotopes

Abstract

ALTHOUGH the separation of the two hydrogen isotopes which occurs on electrolysis must be closely connected with their over-potentials, no measurement of these has been published. A comparison of the deuterium over-potential with that of hydrogen can be of value in elucidating the general mechanism of hydrogen over -potential itself and, as part of an experimental investigation of this, measurements have been made on deuterium. In order to eliminate errors due to the resistance of the electrolyte and to violent gas evolution, it is essential that very low current densities should be used, and the electrolyte must be free from traces of oxygen or dissolved impurities. The over-potential measurements were made under conditions similar to those described in earlier papers¹, but it was a matter of some experimental difficulty to realise these with the small quantities of electrolyte available (1 c.c.). The results obtained with a mercury cathode in a 0.2 N sulphuric acid electrolyte are shown in Fig. 1.