| Abstract
| - On the basis of simultaneous measurements of the electric current and the hydrogen evolution rate, the reactionsat Ni electrodes in alkaline borohydride solutions are successfully decomposed into two component reactions,i.e., borohydride oxidation and hydrogen electrode reaction. The former is a 4-electron anodic reaction withmolecular hydrogen as a product, while the latter is either hydrogen evolution or hydrogen oxidation, dependingon the borohydride concentration and electrode potential. Because of the change of the relative contributionsof these two reactions, the apparent number of electrons in borohydride oxidation changes from 0 to 5 underthe discharge conditions studied, much smaller than the theoretical electron number 8 for full oxidation ofborohydride. The current decomposition result is able to interpret quantitatively the experimental linearrelationship of open circuit potential to logarithmic borohydride concentration. The current decompositionalso reveals a novel phenomenon, i.e., cathodic hydrogen evolution at potentials positive to the normalequilibrium hydrogen potential (called under-potential hydrogen evolution in the present work), and thisobservation is explained by assuming a high energy state of adsorbed hydrogen produced from borohydrideoxidation.
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