Resumo

MARTINEZ, W. M.; FERNANDEZ, A.M.  e  CANO, U.. Caracterización estructural y electroquímica de electrodos de Ni:Zn:S obtenidos por electrodepósito y baño químico para su empleo en electrolizadores alcalinos. Superf. vacío [online]. 2005, vol.18, n.2, pp.14-19. ISSN 1665-3521.

In this work the synthesis of Ni:Zn:S electrodes is described. The electrodes were prepared on a 316 SS substrate, for its use as electrodes in an alkaline electrolyzer. The synthesis of the electrodes consisted on firstly a nickel electrodeposit on 316 SS using a Watt bath and then by a chemical bath technique to deposit a film that turned out to be ZnS. After this, the electrodes were annealed at 3 different temperatures: 200, 250, and 300 ºC in an inert atmosphere. These electrodes were compared among themselves and against electrodes with only electrodeposit and electrodes without annealing.

Studies of XRD show that all electrodes obtained are polycrystalline, and in the case of the nickel electrodes the grain size is of approximately 1 µm (from Scanning Electron Microscopy - SEM). Electrodes in which the chemical bath technique was used, did not show evidence of a ternary compound (i.e. NixZnySz) on the surface. Nevertheless, this compound could be present at the nickel-ZnS interface, for ZnS was observed as wurtzita phase on the suface, which indicates that chemical changes occurred after annealing those samples. By means of Electron Probe X- Ray analysis the presence of nickel oxides were observed on the electrode surface of electrodes with chemical bath, even before the thermal treatment; and when electrochemical tests were carried out with these electrodes, the content of sulfur (S) and zinc (Zn) diminished drastically on the surface of the electrode. Despite this, cyclic voltammetry studies do not show appreciable secondary reactions in the cathodic area, but there is evolution of hydrogen gas in all the electrodes. Also electrodes of Ni:Zn:S annealed at 300°C and 250oC used as cathodes showed acceptable behavior. This was shown by the smaller overpotential for hydrogen evolution compared with that shown by nickel. Chronoamperommetry studies showed that the electrodes have an appropriate stability after 22 hrs.

Palavras-chave : Alkaline electrolysis; Electrodeposit; Nickel electrodes.

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