Electrochemical Formation of a Failure Preventing

Authors: E E Abd El Aal S M Abd El Haleem

Publish Date: 2008/10/21

Volume: 8, Issue: 6, Pages: 557-563

PDF Link

Abstract

Cyclic voltammograms CVs of the Ni electrode are traced in Na2B4O7 solutions as a function of electrolyte concentration voltage scanning range and rate in order to determine the nature of failure protective species formed in the slightly alkaline media The species formed on the Ni electrode are found to depend on the sweep number due to changes in the activation state of the electrode surface The voltammograms are characterized by a pronounced anodic peak due to the formation of NiO and a protective passive film corresponding to the formation of βNiOH2 before the evolution of oxygen An additional anodic peak in the vicinity of oxygen evolution potential appeared in the advanced cycles that is attributed to the transformation of βNiOH2 to βNiOOH The cathodic branch shows only one peak corresponding to the reduction of βNiOOH to βNiOH2 The current density flowing along the anodic oxidation peak varies with the concentration of the electrolyte according to logi textp = a + blogC textB 4 textO 72 where a and b are constants An increase in the scan rate increases markedly the current density flowing along the whole range of the CVs As the concentration of borate anions increases the anodic peak potential is shifted toward more positive values whereas the cathodic peak potential is shifted in the negative direction indicating the irreversibility of formation of the passive film formed on the electrode surface A correlation is made between the anodic oxidation processes and their corresponding cathodic one The failureprotecting film in borate solutions is assumed to be caused by the formation of a sandwich oxide having the form NiO/βNiOH2/βNiOOH

Keywords: