Transport of alkaline cation and neutral species through the alpha-Ni(OH)(2)/gamma-NiOOH film electrode

Abstract

The transport of alkaline cation and neutral species through the alpha -Ni(OH)(2)/gamma -NiOOH film electrode has been investigated during the hydrogen extraction from and injection into the film electrode in 0.1 M LiOH, KOH and CsOH solutions by using the electrochemical quartz crystal microbalance technique combined with the potentiostatic current transient technique and cyclic voltammetry. From the ohmic relationship between the initial current density and the applied potential step, it is suggested that the hydrogen transport through the film electrode is exclusively governed by "cell-impedance". On the basis of 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 the current plateau. After the period of current plateau has finished, it is drastically inserted at an exponential rate. By contrast, during the hydrogen injection, the extraction of alkaline cation is nearly completed before the finish of the current plateau. Most of the neutral species are incorporated into the film electrode during the immersion prior to the hydrogen extraction. The minority is not incorporated until the finish of the current plateau during the hydrogen injection.