Reduction of nitrate ions on Au/Pd/Sn electrode.

L.A. MEIER; S.G. GARCÍA; D.R. SALINAS

Foz do Iguazu, Brazil

Congreso; 6th Spring Meeting of the International Society of Electrochemistry; 2008

International Society of Electrochemistry

Pollution of ground and surface waters by nitrate ions is a common environmental problem throughout intensive agricultural areas. In fact, a high concentration of the nitrate ion has detrimental effects on health and environment, and its removal has gained renewed attention. Possible technologies for the treatment of nitrate ions include ion exchange, biological treatment, reverse osmosis, heterogeneous catalysis and electrochemical reduction. The electrochemical reduction of nitrate ions has been performed using different type of metallic or bimetallic electrodes and, recently, it was indicated that a gold substrate modified with Sn and Pd showed a relatively high activity for this reaction [1].The aim of this work was to prepare and characterize a Au(111)/Sn and Au(111)/Sn/Pd modified surfaces, using conventional electrochemical techniques and STM (Scanning Tunneling Microscopy) technique and to correlate these results with the corresponding activity for the electrochemical reduction of nitrate.Sn nanocristals were formed on the Au(111) surface by the immersion method. Initially, the gold single crystal surface was immersed in 1 mM SnSO4 + 0.5 M H2SO4 deaerated solution under open-circuit conditions for different immersion times, t (5 < t/s < 90), followed by sufficient rinsing with pure water. Then, the electrode was introduced into another electrochemical cell or the STM cell containing 0.5 M H2SO4 supporting electrolyte, at a controlled potential in order to characterize the modified surface. The STM images showed two dimensional islands nucleated on the flat terraces and on step edges. The number and size of these islands increase as the immersion time, t, increases and they tend to merge forming interconnected structures of monatomic high. This type of structure showed practically no catalytic activity for the electroreduction of nitrate when it was used as an electrode in a 0.1 M Na2SO4 + 0.1 M NaNO3  solutionOn the other hand, the subsequent immersion of this type of Au(111)/Sn modified surface in 1mM PdCl2 + 0.1 M Na2SO4 solution produced an increase in the surface activity. This behavior, ascribed as a synergetic effect of Pd and Sn is discussed in the work, considering the surface morphology changes observed by in-situ STM after the immersion in the Pd(II) containing solution.[1] K. Tada, T. Kawaguchi, K. Shimazu, J. of Electroanal. Chem. 572 (2004) 93¨C99.