Transport of hydrogen, alkaline cation and neutral species through $Ni(OH)_2/NiOOH$ film electrode

Abstract

The present work involves the transport of hydrogen, alkaline cation and neutral species through the $Ni(OH)_2$/NiOOH film electrode. In Chapter Ⅲ, the transport of hydrogen, alkaline cation and neutral species through the $α-Ni(OH)_2$/γ-NiOOH film electrode has been investigated in 0.1 M LiOH, KOH and CsOH solutions by employing potentiostatic current transient technique and cyclic voltammetry combined with electrochemical quartz crystal microbalance (EQCM) technique. From the ohmic relationship between initial current density and applied potential step, it is suggested that the hydrogen transport through the $α-Ni(OH)_2$/γ-NiOOH film electrode is exclusively governed by ``cell-impedance``. Based upon the ``cell-impedance controlled`` hydrogen transport, the mass change measured indicates that during the hydrogen extraction, the alkaline cation is slowly inserted into the film electrode before the finish of current plateau. After the period of current plateau is finished, it is drastically inserted in an exponential rate. By contrast, during the hydrogen injection, the extraction of alkaline cation is nearly completed before the finish of current plateau. Most of the neutral species are incorporated into the film electrode during the preceeding immersion stage prior to the hydrogen extraction. The minority is not incorporated until the finish of current plateau during the succeeding hydrogen injection. In Chapter Ⅳ, the hydrogen transport through the $β-Ni(OH)_2$/β-NiOOH film electrode has been explored in 0.1 M KOH solution by using cyclic voltammetry and potentiostatic current transient technique. From the linear relationship between initial current density and applied potential step, it is suggested that the hydrogen transport through the $β-Ni(OH)_2$/β-NiOOH film electrode proceeds under the ``cell-impedance controlled`` constraint. The anomalous behaviours of the anodic current transient including the occurrence of current peak can be accounted for in t...