On the electrooxidation and amperometric detection of NO gas at the Pt/Nafion® electrode

The electrochemical oxidation of nitric oxide (NO) gas at the Pt/Nafion(R) electrode has been studied at a concentration of 500 ppm. The electrooxidation of NO taking place over a wide potential range can be described by a transcendental equation, from which the half-wave potential of the reaction can be determined. For NO oxidation with appreciable overpotentials but negligible mass-transfer effects, the Tafel kinetics applies. The obtained charge transfer coefficient (alpha) and the exchange current density (i(o)) are 0.77 and 14 muA/cm(2), respectively. An amperometric NO gas sensor based on the Pt/Nafion(R) electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm. The Pt/Nafion(R) electrode was used as an anode at a fixed potential, preferably 1.15 V (vs. Ag/AgCl/sat. KCl), which assures current limitation by diffusion only. The sensitivity of the electrochemical sensor was found to be 1.86 muA/ppm/cm(2). The potential interference by other gases, such as nitrogen dioxide (NO2) and carbon monoxide (CO), was also studied in the range 0-500 ppm. Both sensitivity for NO and selectivity of NO over NO2/CO show significant enhancement upon using a cyclic voltammetric (CV) activation, or cleaning procedure.