Self‐Discharge of the Nickel Electrode in the Presence of Hydrogen: I. Textural Study

Self‐Discharge of the Nickel Electrode in Presence of Hydrogen: II. Electrochemical Approach

“…(ii) a chemical reduction of NiOOH by hydrogen in agreement with our previous finding, 1 which could obey the following equation…”

“…Among the possible mechanisms during Ni/H 2 cells self-discharge is the electrochemical reduction of charged material, as proposed by Lim et al 2 Within such a mechanism, the rate-controlling step is expected to be the oxidation of hydrogen (the nickel substrate playing the role of catalyst or not). Therefore, the relation governing its kinetics should be of first order with respect to the hydrogen pressure expressed as follows ln P(H 2 ) ϭ k 1 t ϩ k 2 [1] with k 1 being the reaction rate constant for the catalytic oxidation of hydrogen. To check if such a mechanism can be used to describe our observed self-discharge variation for resting times greater than 100 h, the logarithm of pressure was plotted as a function of the open-circuit time.…”

“…We previously confirmed, through a structural/textural study, that the large self-discharge rate in Ni/H 2 cells originates from a hydrogen-nickel oxyhydroxide interaction that results in the reduction of either ␥or ␤-NiOOH phases into the ␤(II) phase. 1 In addition, we noted that the reduction kinetics were strongly dependent upon the experimental parameters. To our knowledge, despite several studies, the rate law controlling self-discharge in Ni/H 2 cells has not yet been clearly established.…”

“…Indeed, two oxidized NiOOH phases denoted ␤(III) and ␥(III) may be present in various amounts in a nickel hydroxide electrode depending on its state of charge. 8 In our previous paper, 1 we have demonstrated that water-dissolved hydrogen enables the reduction of both ␤(III) and ␥(III) phases. In addition, the reaction rate was shown to increase significantly with increasing tem-perature in the presence of hydrogen.…”

Nickel Hydroxide “Stacks of Pancakes” Obtained by the Coupled Effect of Ammonia and Template Agent

“…Sticking to the nickel hydroxide system, results that can be related to ours are scarce. Sac Epe ´e et al 19 prepared β(III) and γ(III) nickel oxyhydroxides to study their reduction in the presence of hydrogen. The precursor R-Ni(OH) 2 was obtained by adding Ni(NO 3 ) 2 to ammonia, and processed into β-Ni(OH) 2 under hydrothermal conditions (125 °C, 6 h).…”