Analysis of stresses generated during hydrogen extraction from and injection into Ni(OH)(2)/NiOOH film electrode

Stresses generated during the hydrogen extraction from and injection into a Ni(OH)(2)/NiOOH film electrode in 0.1 M KOH solution are analysed by means of a laser beam deflection technique combined with potentiostatic current transient and electrochemical quartz crystal microbalance (EQCM) techniques . From the measured values of the film thickness, the elapsed time for phas e boundary movement (PBM) and the potential step given between the hydrogen extraction/injection potential and the plateau potential, the velocity and the mobility of PBM are determined to be 2.3 X 10(-6)-5.4 X 10(-6) cm s(-1 ) and 3.5 X 10(-10)-2.6 X 10(-9) cm(2) s(-1) V-1, respectively. From the ma ss change measured by means of EQCM, it is suggested that, during hydrogen extraction, the PBM continues until the insertion of K+ ions begins to occu r simultaneously with the desertion of such neutral species as H2O molecule s or KOH molecules. During hydrogen injection, the PBM is accompanied by th e extraction of K+ ions, followed by the insertion of neutral species. From the mass change transient and the deflection transient, simultaneously mea sured with the current transient, it is suggested that the sharp rise of te nsile and compressive deflections in the initial stage is traced back to th e PBM. The following relaxation of tensile and compressive deflections is a ttributed to the extraction/insertion of neutral species. Most of the stres ses developed during the hydrogen extraction and injection originate mainly from the PBM, not the extraction/insertion of K+ ions and neutral species. (C) 2000 Elsevier Science S.A. All rights reserved.