Abstract
On the assumption that low hydrogen overpotential of cobalt plating is due to the peculiar crystal structure of electro-deposited intermetallic compounds, the relationship between the crystal structure and hydrogen overpotential was exammined by X-ray diffraction method. When above 8×10-3mol/dm3 of vanadium pentoxide was added into the citrate cobalt plating bath, an intermetallic compound, σ-CoV, was obtained reproducibly. X-ray diffraction pattern of σ-CoV, however, disappeared by annealing the electrodeposit at 500°C for 1h. Low hydrogen overpotential seems to be due to the σ phase of the electro-deposit; σ phase was stable in hydrogen evolution by electrolysis of NaOH solution. By addition of molybdenum, electrodeposited cobalt became amorphous.
