Influence of the concentration and the nature of the supporting electrolyte on the electrochemical reduction of nitrate on tin cathode

The influences of the potential, the concentration and the nature of the supporting electrolyte on the rate of the reduction of nitrate on tin were studied by both voltammetry and constant potential electrolytic experiments. Both the rate of the reduction of nitrate and the yield of nitrogen increase as the negative potential increases from −1.8 to −2.8 V versus Ag/AgCl, while the yield of nitrite decreases. The yield of ammonia displays a maximum at −2.4 V and consequently decreases. The rate of the reduction at −1.8 V versus Ag/AgCl increases significantly as the concentration of NaCl increases. The cation of the supporting electrolyte increases the rate of the reduction along the series Li+ < Na+ < K+ < Cs+. Higher rates than that of the alkalimetals have been obtained in the presence of ammonium as well as of multivalent cations such as Ca2+ and La3+. The anion of the supporting electrolyte decreases the rate of the reduction in the order I− > Br− > Cl− > F− at −1.8 V. The experimental results were qualitatively explained by the Frumkin theory and additionally by the theory of the formation of ion pairs between the cation of the supporting electrolyte and the reacting nitrate.