AN AMPEROMETRIC SOLID-STATE SENSOR FOR NITROGEN-DIOXIDE BASED ON A SOLID POLYMER ELECTROLYTE

A new sensor is described consisting of a Nafion membrane to which a very fine gold square grid indicator electrode is mechanically pressed. A platinum counter and a Pt/air reference electrode are prepared on the membrane using a chemical plating method. Nitrogen dioxide was determined in air by reduction at -0.3V vs. Pt/air electrode (0.75 V vs. SHE). The response dependence on the NO2 concentration was linear, with a sensitivity of 59 nA.ppm-1 (42% rel. humidity). The time constant and the time required to attain 95% of the steady-state response were 2.2 and 10 s, respectively. The response was independent of the air flow rate, but increased linearly with increasing relative humidity. The sensor sensitivity decreased with time-the longer the sensor was in contact with NO2. The decrease amounted to ca. 5% per 24 hours during constant exposure to NO2. The indicator electrode can be reactivated by cyclic polarization. On the basis of the sensitivity attained, the indicator electrode can be considered as an array of microband electrodes.