The hydrogen-electrode reaction in the isotopically mixed system—II. Evaluation of the electrolytic separation factor of deuterium from the rest potential of the hydrogen electrode in the deuterium-containing system

The rest potential, E_r, of the hydrogen electrode in deuterium-containing hydrogen and a solution of light water as referred to the reversible hydrogen electrode in the light hydrogen and the same solution is formulated as a function of deuterium content of the gaseous hydrogen and the deuterium separation factor, S_b, in the hydrogen ionization reaction. It is shown that the relation is not significantly affected by the operative mechanism of the hydrogen-electrode reaction. Consequently, the relation provides a convenient method of evaluating S_b from the observation of E_r.

Experiments were carried out on Pt, Ni, Au and Ag in the system composed of deuterium-containing hydrogen and light water. The value of S_b as evaluated from E_r was practically independent of the deuterium content in the gaseous hydrogen. The values obtained were 1·1 for Pt in acidic and alkaline solutions, 1·6 for Ni in alkaline solution, 1·2 for Au and 1·5 for Ag, both in acidic solution. These values multiplied by the partition coefficient of deuterium between hydrogen and water (4·0 at room temperature) give approximate values of the deuterium separation factor in the hydrogen evolution reaction.