Solid-state microelectrode oxygen sensors

• Published in: Analytica chimica acta 1999-05, Vol.388 (1), p.51-62
• Main Authors: Sotiropoulos, Sotiris, Wallgren, Kirsi
• Format: Article
• Language: English
• Subjects: Amperometric sensors; Analytical chemistry; Chemistry; Exact sciences and technology; Gas sensors; General, instrumentation; Oxygen reduction; Solid polymer electrolyte
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/S0003-2670(99)00119-1

Two types of all-solid amperometric sensors, incorporating Nafion ® as the solid ionic conductor and exhibiting microelectrode behaviour, have been used as gaseous oxygen probes in the 1–25% (v/v) concentration range. The first one involved a Pt or Ag microdisc surrounded by a ring of the anode material, the two electrodes being in the same plane and covered by a solution-recast Nafion ® film. In a modified version of this type of sensor, a Au microband was used as the indicator electrode. Well-defined sigmoidal voltammograms for oxygen reduction from the gas phase were obtained and, when used in a constant potential mode, the sensing device showed good linearity ( r 2=0.9998–0.9988) with oxygen concentration in the gas stream and a satisfactory sensitivity of 8×10 −5 A cm −2 (%v/v) −1. The high detection limit of 2% (v/v), however, restricts the possible applications to crude monitoring in the higher oxygen concentration range. In the second type of sensor, Au electrodes were vacuum-deposited as thin layers on the same face of a Nafion ® membrane and a strip of uncovered ionic polymer between the two metal layers ensured completion of the electrical circuit. The gas samples were in contact with the electrode layers and oxygen reduction led to an exponential current rise over a wide potential range indicating very high mass transport rates. The sensitivity of the device was 20 nA (%v/v) −1 and it is suggested that with such a sensor configuration the electroactive gas reacts at the line formed by the gas/solid electrolyte/metal layer interface, i.e. at a virtual microband electrode.