Kinetic studies of reduction of nitrate ions at Sn-modified Pt electrodes using a quartz crystal microbalance

An electrochemical quartz crystal microbalance (EQCM) was used to determine the surface coverage of adsorbed nitrate during the reduction of nitrate on Sn-modified Pt electrodes. The rate equation was derived as a function of the surface coverage of nitrate, the concentration of hydronium ion and the electrode potential for an electrode with a tin coverage of ca. 0.35, which showed the highest activity of the electrodes reported so far. N2 (30%) and NH4+(62%) were produced. From the Tafel slope at a constant surface coverage (−0.115 V decade−1) and the reaction orders (1.1 and 0.94 with respect to the surface coverage of the adsorbed nitrate and the concentration of hydronium ion, respectively), it is concluded that the rate-determining step is the reaction of the adsorbed nitrate with the hydronium ion and an electron.