Formation of volatile products during nitrate reduction on a Sn-modified Pt electrode in acid solution

Nitrate reduction is investigated in acid solution on Sn-modified Pt electrodes with different Sn coverages. Volatile products and intermediates were detected by means of on-line electrochemical mass spectroscopy. N2O is found as the main product for intermediate coverages of Sn whereas NO is the dominant product for high Sn coverages. By comparison to N2O reduction on Pt and Sn-modified Pt electrodes with intermediate and high Sn coverages, respectively, N2 formation is proposed to result from the consecutive reduction of N2O on free Pt sites on the PtSn surface. In addition, chemical reactions between ammonia, hydroxylamine and nitrite are also briefly studied as possible reaction steps leading to N2O and N2 during nitrate reduction.

► A partial coverage of tin on platinum promotes the reduction of nitrate.
► A low amount of tin on platinum primarily leads to N2O as volatile product.
► A high amount of tin on platinum primarily leads to NO as volatile product.
► Dinitrogen N2 is formed slowly through the reduction of N2O on free platinum sites.
► Solution reactions to volatile products may be important in long-term electrolysis.