Abstract
A single crystal of Mo (100) was polarized in at 25°C. The electrode was a rotating disk electrode with a rotation rate of 1000 rpm. The composition of the surface was analyzed by electron spectroscopy for chemical analysis (ESCA). Molybdenum is passive in range −480 to 160 mV (SCE). The polarization curve does not show any active dissolution peak before passivation. The ESCA analysis shows that Mo is passivated by chemisorption of a monolayer of oxygen; no three‐dimensional oxide is formed on the surface in the passive range. Oxygen adsorbed on the surface of Mo increases the hydrogen reaction. The Tafel slope is found to be 120 mV/decade, and the hydrogen reaction is controlled by the Volmer‐Tafel mechanism. For oxygen free surface the Tafel slope is 70 mV/decade. In the transpassive region at potentials above 160 mV (SCE) the anodic current increases rapidly and a layer of a multivalent molybdenum‐oxygen compound is formed on the surface.
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