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

Kuo-Chuan Ho,Wen-Tung Hung,Jin-Cherng Yang

doi:10.3390/s30800290

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.

Highlights

Nitric oxide (NO) gas, which is released from automobiles and combustion facilities, is a toxic gas
The anodic peaks at E > 0.6 V are ascribed to the surface oxide formation and the cathodic peak at E ≈ 0.43 V is ascribed to the surface oxide reduction
This work reported on the electrooxidation of NO gas at the Pt/Nafion® electrode and on the amperometric NO sensing based on the same electrode

Summary

Introduction

Nitric oxide (NO) gas, which is released from automobiles and combustion facilities, is a toxic gas. The sensing characteristics of NO oxidation at the Pt/Nafion® interface, including the operating potential, sensitivity, and interfering gases (NO2 and CO), were studied in the high concentration range of 0-500 ppm. To maintain the electrode/electrolyte interface in an activated state, the Pt/Nafion® (sensing) electrode used in this study was activated by repeated potential cycling for the purpose of cleansing. This was done in a cell containing 0.5 M H2SO4 by scanning the electrode potentials between -0.2 and 1.4 V for 10 cycles at a scan rate of 20 mV/s under N2 at a flow rate of 200 ml/min.

Results and Discussion

H A1 H A2

Conclusion