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

To investigate the self-discharge mechanism in Ni/H-2 cells, the interactio ns of hydrogen with the beta-NiOOH and gamma-NiOOH nickel oxyhydroxide phas es were simulated in a water-loaded autoclave as functions of both temperat ure and pressure, Under such conditions, X-ray diffraction measurements cou pled with transmission electron microscopy showed that both gamma(III) and beta(III) phases are reduced to a beta(II) phase, thus providing direct evi dence 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 beta-NiOOH and gamma-NiOOH phases, followed by dissolved hydrogen reductio n concomitant with an oriented nucleation growth of the reduced phase on th e intact NiOOH, is proposed to account for the self-discharge mechanism obs erved in the autoclave. (C) 1999 The Electrochemical Society. S0013-4651(98 )10-016-2. All rights reserved.