Influence of Humidity on Parameters of Amperometric Sensor with Nafion Membrane

The paper presents the results of investigation on influence of moderate and high relative humidity (RH) on the signal, sensitivity and response time of prototype sulphur dioxide sensor with Nafion membrane. Gold electrode vacuum sublimation deposited on the Nafion membrane surface was a working electrode. Additionally, impedance investigations were carried out in the potential range, within which the mechanism of sulphur dioxide oxidation is activation and diffusion controlled. The parameters corresponding to mass and charge transfer were determined based on a proposed equivalent circuit. Potentiostatic and impedance investigations revealed diverse influence of humidity on the sensor. For low and moderate RH (33% and 54%) the sensor exhibited higher sensitivity (0.6 A/ppm and 0.68 A/ppm respectively) and shorter response time (8 s) to changes of analyte concentration as compared to the sensor exposed to RH 0% (0.52 A/ppm and 14 s). Impedance measurements for low and moderate showed that the parameters characterizing mass and charge transfer took lower values than the corresponding parameters of the sensor operating at RH 0%. Ratio of diffusion resistance to activation resistance for the potential 700 mV, determined using the electrical equivalent circuit is: 2.3 Hz^0.5 for RH 0%, 2.0 Hz^0.5 for 33%, 2.0 Hz^0.5 for 54%, 2.8 Hz^0.5 for 76%, 3.4 Hz^0.5 for RH 86%.