Effect of Multivalent Cations upon Reduction of Nitrate Ions at the Ag Electrode

Cathodic reduction of nitrate ions at a polycrystalline silver electrode was reexamined, particularly, in the presence of La 3 + and Al 3 + 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 La 3 + ions, was observed, resulting in a large positive shift of the voltammetric peak associated with nitrate reduction. Electrochemical quartz crystal microbalance measurements demonstrated formation at the electrode surface, close to the onset potential for NO 3 − reduction, of films assigned to La ( OH ) 3 and/or Al ( OH ) 3 in the solutions containing La 3 + and Al 3 + ions, respectively. The observed effect of La 3 + ions upon nitrate reduction is explained in terms of acid‐base catalysis, involving species diffusing as La(III)‐nitrate complexes (ion pairs) close to the silver electrode.