The electrocatalytic activity of An electrodes modified with thiourea (TU), urea (U), iodide ions (I-) and sulfide ions (S2-) towards reduction of NO3- to NH3 have been tested. Cyclic voltammetry (CV) of the TU/Au electrode in 0.5 M NaNO3 (N-2-saturated, pH 12.5) revealed an increase of the reduction peak of NO3- at ca. +0.75 V versus reversible hydrogen electrode (RHE) more than at the bare (i.e., unmodified) An electrode. On the other hand, the intensity of this peak is more depressed at I-/Au, S-2(-)/Au and U/Au electrodes. The Tafel slope is almost the same for the two reactions, i.e., the hydrogen evolution reaction (HER) and the nitrate reduction reaction suggesting a common rate-determining step (r.d.s.) for both reactions. Galvanostatic electrolysis of the basic nitrate solution resulted in three major reduction products i.e., NH3, NO2- and H-2. The TU/Au electrode showed the highest current efficiency, Q, of the NH3 production (about 85%), which is about 6.5 times higher than that of the NO2- production. While the I-/Au and S2-/Au showed a sharp increase in the cur-rent efficiency for the hydrogen evolution reaction to about 43 and 47%, respectively, with a concurrent depression of the total current efficiency of the nitrate reduction. (C) 2003 Elsevier Ltd. All rights reserved.