The electrochemical reduction of carbon dioxide is strongly catalysed when it is carried out by cathodically generated and continuously recycling nickel(O) from the nickel(II)-bipyridyl precursor complex. In such a way, equimolar amounts of carbon monoxide and carbonate ions are obtained in a good yield referred to the charge transferred. However, by performing this process under controlled potential conditions, unsatisfactorily low turnover numbers are found because these reduction products are able to abstract progressively the nickel promoter from the electrocatalytic cycle. Carbonate ions in fact enter the coordination sphere of nickel(II), giving a mixed complex which can be reduced at potentials more negative than the precursor species, while carbon monoxide reacts with nickel(O) leading to the formation of a quite inert carbonyl-bipyridyl compound. The negative effect of these side reactions can be overcome by performing this electrocatalytic process at constant current in a cell without any diaphragm separating the two electrode compartments. A reaction pathway is proposed which is consistent with the data obtained. © 1987.
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