XRD studies of nickel hydride formation in alkaline solutions containing a promotor

An effect of cathodic charging conditions on the amount of the β-NiH_x phase formed in nickel electrode in alkaline solutions was studied by means of X-ray diffraction technique. Electrolytic nickel coatings on copper substrate were hydrogenated in KOH, NaOH, LiOH and NH₄OH solutions containing promoters such as As₂O₃, Sb and GeO₂. Dependences of the β-NiH_x phase volume fraction on the promotor concentration, charging current density and charging duration were studied. Optimal values of these charging conditions parameters were determined. The volume fraction of the β-NiH_x phase amounted up to ∼56% of 10 μm thick nickel coating. The quantity of nickel hydride did not depend on the alkali and its concentration. Promoters were arranged in the following order of effectiveness in causing nickel hydride formation: S>As>Sb>Ge. It was suggested that NiAs type compounds could take part in the nickel hydride formation.