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1 2004

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Electrochemical Synthesis and Properties of Micro- and Nanocrystallites of Cobalt

Wiśniewski A., Paklepa P., Wrona P.

Polish Journal of Chemistry

2004

Vol. 78 / nr 9

1327-1337

The electrochemical synthesis of cobalt particles has been performed by electroreduction of Co(II) ions on the mercury electrode at potentials about -1.4 V vs. SCE. The electroreduction of Co(II) observed in cyclic voltammetry (CV), was a totally irreversible process due to the formation of an unstable cobalt amalgam, which decomposed into metallic cobalt. It has also been observed that metallic cobalt, practically insoluble in mercury, tends to aggregate, forming nanocrystallites and clusters that finally separate from mercury in the form of a black powder. The black cobalt powder, obtained this way, has been characterized using scanning electron microscope (SEM) imaging, X-ray analysis and specific surface measurements (nitrogen adsorption according to BET isotherm). The results of these experiments indicate that the cobalt powder obtained from the amalgam consists of partially oxidized crystallites of dimensions less than 20 nm. These nanocrystallites form aggregates of dimensions up to several or more _m. Due to their specific surface exceeding 30 m2/g, such crystallites can be used for the preparation of metallic catalysts.Ahypothesis, concerning the nucleation and further aggregation of Co from a homogeneous cobalt amalgam, leading to the formation of nanocrystallites, is discussed according to the burst-nucleation theory.