Reduction of nitrate ion was investigated on copper and polypyrrole coated copper electrode (PPy-Cu) in acidic aqueous medium. The nitrate concentration was increased, from 5 to 200 Mm (0.1 M LiClO4 + 0.001 M HCIO4 + x mM KNO3; x = 5, 20, 50, 100 and 200 mM). The applied potentials were -0.4, -0.6, -0.8, -1.0 and -1.2 V [Ag/AgCl]. Depending on these parameters, nitrate reduction gave the same products with different concentrations on blank Cu and on PPy-Cu. On blank Cu, nitrite ion was formed under almost any condition whereby on PPy-Cu, ammonia was the main product. Especially at low overpotentials, such as -0.4, -0.6 and -0.8 V no nitrite was detected on PPy-Cu which leads to the conclusion that the coating of the surface changes the reaction mechanism. (C) 2014 Elsevier B.V. All rights reserved.