FORMATION OF THE NICKEL HYDRIDE AND ITS ANODIC BEHAVIOR

The formation of the nickel hydride during cathodic polarization of nickel in a sulfuric acid solution with an admixture of thiourea and its anodic behavior were studied by a combined electrochemical and radiometric technique. The nickel hydride NiH0.5 was shown to form as a result of hydrogen absorption by nickel at i(c) greater-than-or-equal-to 1 mA/cm2. We measured thickness of the hydride layer as a function of the cathodic current density and duration of the cathodic polarization, as well as the total amount of absorbed hydrogen and its distribution over the depth of the hydrogen-charged sample. During anodic polarization, the hydride uniformly dissolves at a sufficiently large anodic current density (i(a) greater-than-or-equal-to 2 x 10(-4) A/cm2), whereas at smaller anodic current densities the selective ionization of hydrogen (formed during the solid-state decomposition of NiH0.5) occurs. The nickel hydride formation was shown to be limited by hydrogen diffusion through the hydride layer.