Influence of the electrode and the pH on the rate and the product distribution of the electrochemical removal of nitrate.

The effect of the nature of six metal electrodes (Sn, Bi, Pb, Al, Zn, In) on the rate and the distribution of the products of the electrochemical reduction of nitrate was studied. The product distribution depends on the nature of the metal only quantitatively, while the rate of the reduction was found to be about the same on all metals when the electrolysis was performed at the same rational potential (E(r)), which is the difference between the applied potential and the potential of zero charge of each metal. Based on these results it was concluded that the mechanism of nitrate reduction is the same for all cathodes studied. Additionally, the influence of the initial pH on the rate of the reduction of nitrate and the selectivity of the products on a tin cathode was studied. The rate of the reduction increases linearly with the concentration of hydronium ion in the pH range 0-4, whereas it is not dependent on the pH at higher pH values. The main products at pH > 4 were nitrogen, nitrous oxide, ammonia and nitrite, while at pH 0-4 ammonia and hydroxylamine were mainly formed.