Abstract
The electroreduction of nitrate ions is investigated in acid and neutral aqueous solutions (HClO4 and NaClO4 as electrolytes) at polycrystalline copper electrodes, copper single crystals and at copper particles deposited in polyaniline (PANI) layers. In the presence of low nitrate concentrations (5 mM), the reduction of nitrate is not significantly different on various copper atomic surface structures but is greatly dependent on the local pH at the electrode. In contrast to strong acidic solutions, two separate waves are detected when nitrate ions are present in neutral solutions irrespective of the use of copper polycrystalline or single crystal electrodes. The first of the two waves leads to the formation of nitrite ions. When copper particles are dispersed in polyaniline layers it is demonstrated that the electrocatalytic activity is strongly dependent on the way of depositing copper in the polymer layer. A clear difference is observed in the current response in absence and presence of nitrate ions for copper deposited in the reduced state of the PANI layer, whereas copper deposited in the oxidized state of the PANI layer remains still electrocatalytically rather inactive. Copper crystalline species act effectively for the investigated reaction only if copper conducting paths are available through the polymer matrix up to the underlying metal surface.
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