ELECTROCATALYSIS OF ANODIC OXYGEN-TRANSFER REACTIONS - OXIDATION OF AMMONIA AT ANODIZED AG-PB EUTECTIC ALLOY ELECTRODES

Ammonia (NH3) in alkaline media is oxidized to NO3- at anodized Ag-Pb eutectic alloy electrodes (2.4% Ag by weight). The anodic signal is diminished for pH < ca. 8, and this attenuation is attributed to the protonation of NH3 to form NP4+. Protonation of NH3 is concluded to prevent adsorption of the NH3 at silver sites in the electrode surface as the initial step in the electrocatalytic oxidation mechanism. For pH > ca. 10, the anodic signal decreases with time because of the loss of NH3 by volatilization. The heterogeneous rate constant for oxidation of NH3 to NO3- is significantly smaller than that for oxidation of ethylamine (EA) to acetaldehyde and NH3 (k(app,NH3)/k(app,EA) = similar to 0.2). Hence, NH3 is concluded to be a product of ethylamine oxidation at a rotated disk electrode whereas acetaldehyde and NO3- are the final products of the exhaustive acetald electrolysis of ethylamine.