On the Electrooxidation and Amperometric Detection of NO Gas at the Pt/Nafion^® Electrode

Abstract: The electrochemical oxidation of nitric oxide (NO) gas at the Pt/Nafion^® 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 (a) and the exchange current density (io) are 0.77 and 14 mA/cm², respectively. An amperometric NO gas sensor based on the Pt/Nafion^® electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm. The Pt/Nafion^® 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 mA/ppm/cm². 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.