Nitrate reduction on tin-modified rhodium, ruthenium, and iridium electrodes

The reduction of nitrate ion was conducted on Sn-modified rhodium, ruthenium, and iridium electrodes in 0.1 M HClO4. These electrodes showed very high electrocatalytic activities for this reaction, although they were not as high as those of the previously reported Sn-modified palladium and platinum electrodes. The number of cleaved N-O bonds per reduced nitrate ion was calculated from the product distribution to be 2.2-2.5, independent of the noble metal including Pt and Pd. These results show that Sn-modified noble metal electrodes (Rh, Ru, It, Pd, and Pt) are good catalysts for N-O bond cleavage. On the other hand, the product strongly depends on the electrode. The main product formed at -0.2 V vs. Ag/AgCl on Sn/Rh was N2O (59%), while the remaining products were hydrogenated species such as NH3+ OH (22%) and NH4+ (19%). On Sn/Ru, only hydrogenated products were formed; NH3+ OH: 46%, NH4+: 41%. Sn/Ir showed a product distribution similar to that on Sn/Pt; N-2 (17%), NO2- (17%), N2O (11%), and NH3+OH (56%). The potential of the electrodes for the selective N-2 formation, calculated on the basis of the number of cleaved N-O bonds, and formed N-N and N-H bonds per reduced nitrate ion, decreased in the order of Sn/Pd > Sn/Rh > Sn/Pt > Sn/Ir > Sn/Ru, although the highest N-2 production was obtained on Sn/Pt. (c) 2009 Elsevier B.V. All rights reserved.