Effect of multivalent cations upon reduction of nitrate ions at the Ag electrode

Cathodic reduction of nitrate ions at a polycrystalline silver electrode wa s reexamined, particularly, in the presence of La3+ and Al3+ cations in the solution. Although the onset potential for this reaction is located above the zero charge potential of Ag, a marked catalytic effect of La3+ ions, wa s observed, resulting in a large positive shift of the voltammetric peak as sociated with nitrate reduction. Electrochemical quartz crystal microbalanc e measurements demonstrated formation at the electrode surface, close to th e onset potential for NO3- reduction, of films assigned to La(OH)(3) and/or Al(OH)(3) in the solutions containing La3+ and Al3+ ions, respectively. Th e observed effect of La3+ ions upon nitrate reduction is explained in terms of acid-base catalysis, involving species diffusing as La(III)-nitrate com plexes (ion pairs) close to the silver electrode. (C) 1999 The Electrochemi cal Society. S0013-4651(98)08-073-2. All rights reserved.