Electroreduction of nitrate ion to nitrite and ammonia on a gold electrode in acidic and basic sodium and cesium nitrate solutions

The electroreduction of NO3- to NO2- and NH3 has been investigated using a polycrystalline Au electrode in 0.5 M NaNO3 and CsNO3 solutions with pH in the ranges 1.1-3.0 and 9.85-12.8. The reduction of NO3- does not occur significantly in the strongly acidic solutions with pH lower than 1.4 to 1.6: the current efficiency for the NO3- reduction is less than 5%. A further increase in pH significantly facilitates the NO3- reduction. In basic solutions the reduction of NO3- occurs predominantly: the current efficiency reaches the range 80 to 99%. In the case of NaNO3 solutions the ratio of the current efficiencies for NH3 and NO2- production, CENH3/CENO2- is nearly unity in the acidic solutions and 2 to 3 in basic solutions. On the other hand, in CsNO3 solutions, the current efficiency of NO2- production becomes much higher and the CENH3/CENO2- is 1 to 0.5 at pH in the range 2.0-3.0 and 0.2 to 0.5 at pH in the range 10.0-12.7. Partially positively-charged Na or Cs adatoms underpotentially deposited (upd) on the Au electrode surface are believed to facilitate the adsorption of NO3- ions, resulting in the preferential reduction of NO3-. (C) 1999 Elsevier Science S.A. All rights reserved.