Self-discharge of the nickel electrode in the presence of hydrogen. I. Textural study

To investigate the self-discharge mechanism in Ni/H2 cells, the interactions of hydrogen with the β-NiOOH and γ-NiOOH nickel oxyhydroxide phases were simulated in a water-loaded autoclave as functions of both temperature and pressure. Under such conditions, X-ray diffraction measurements coupled with transmission electron microscopy showed that both γ(III) and β(III) phases are reduced to a β(II) phase, thus providing direct evidence of hydrogen-nickel oxyhydroxide chemical interaction in charged Ni/H2 cells. The kinetics for such a reaction were found to be mainly controlled by temperature rather than hydrogen pressure. Partial dissolution of solid β-NiOOH and γ-NiOOH phases, followed by dissolved hydrogen reduction concomitant with an oriented nucleation growth of the reduced phase on the intact NiOOH, is proposed to account for the self-discharge mechanism observed in the autoclave