Oxidation of nitrites on solid electrodes - I. Determination of the reaction mechanism on the pure electrode surface

The electrochemical behavior of nitrite ions on gold, platinum, and glassy carbon (GC) rotating electrodes was investigated. It was observed that the oxide layer formed on the platinum and gold electrode surfaces hinders the nitrite oxidation process. The use of different solid electrodes allowed the determination of the conditions under which an elucidation of the reaction mechanism is possible. Those are the conditions when the oxide layer does not exist or its effect is negligible. The gold (for pH<6) and the GC electrode (GCE) (for pH<12) appeared to be suitable for this purpose. Our investigations confirmed the reaction mechanism in which the overall oxidation of NO2- to NO3- consists of the charge-transfer step NO2--->NO2 + e(-), followed by the homogeneous disproportionation of NO2 :2NO(2) + H2O-->NO2- + NO3- + 2H(+). The value of the rate constant of the homogeneous disproportionation reaction, k, was established to be (0.11+/-0.01) x 10(7) mol(-1) dm(3) s(-1). Calculations were based on the experiments performed for different nitrite concentrations and different rotation speeds, over a wide range of pH. The results obtained for the gold and the GCE were almost the same. The obtained values of the formal potential E-0(NO2-/NO2) = 0.78 +/- 0.006 V, are in agreement with those reported in the literature. (C) 2002 The Electrochemical Society. [DOI: 10.1149/1.1433751] All rights reserved.