THE BEHAVIOUR OF MOLYBDENUM ON CATHODIC POLARISATION WITH REFERENCE TO THE EFFECT OF ANIONS ON ITS HYDROGEN OVERPOTENTIAL

The overpotential of hydrogen is measured in pure HCl solution of concentration ranging front 5.91 — 0.003N. Within this concentration range and at current densities = 1 x10⁵ — 1.8 x 10^-4 amps./cm² the Tafel-line slope amounts to 0.006, which suggests a dual electrochemical-catalytic mecha­nism. At lower acid concentrations than 0.1 N and at higher currents than 1.8 X 10^-4, the Tafel-line slope increases continuously up to 0.116 is 0.003 N-HCI. Borate and nitrate ions possess a pronounced effect on the slope of the Tafel lines, but the effect of phthalate is small.