Popis: |
The growth kinetics of thin anodic oxide films at nickel electrodes are examined in 0.1 N KOH solutions at room temperature under potentiodynamic and galvanostatic conditions. At electrodes that have been mechanically polished and cathodically reduced, growth of the lower oxidation state phase, β-Ni(OH) 2 , follows, under both experimental conditions, the formalism of the Cabrera—Mott model of high field assisted formation of thin oxide films. At 10 −3 Acm −2 , the field within the oxide phase is 8.5 × 10 6 V/cm. The field decreases 1.3 × 10 6 V/cm for each ten-fold decrease of current density. The potential at which β-Ni(OH) 2 begins to grow, V 0 = −0.39 V vs she , is identified as the reversible potential of the phase. It is, however, 270 mV positive than the reversible potential listed in literature for Ni(OH) 2 formation in solutions of the same pH. It is suggested that the observed reversible potential refers to the β-Ni(OH) 2 phase. The exchange current density for the oxide film growth is 2.3 × 10 −10 Acm −2 . Comparison of the kinetics at Pt and Ni electrodes indicates that the activation energy for the growth of the β-Ni(OH) 2 phase is 21 kcal/mole. |