Amperometric Oxygen Sensor Using NAFION Membrane

Abstract

An approach to an amperometric oxygen sensor operative at room temperature was conducted through three types of sensor elements using NAFION membrane (Figs.1 and 10( a )). With an electrochemical cell consisting of a sheet of NAFION membrane and a couple of Pt black electrodes (sensor A), it was necessary to supply H₂ over the counter electrode to obtain a sensing signal to oxygen (Fig.3). The short-circuit current of the sensor increased with increasing oxygen partial pressure (Fig.2). The open-circuit voltage (electromotive force)varied logarithmically with the partial pressures of oxygen and hydrogen with theoretical slopes of an H₂-O₂ fuel cell (Fig.5). As a next step, a pair of the above type elements were laminated with a porous spacer sandwiched in between (sensor B), where the inner cell was designed to function as a hydrogen self-generation system at an external voltage above ca. 0.8V(Fig.6). The short-circuit current of the outer cell of sensor B was found to increase with increases in the oxygen partial pressure in the gas phase as well as dissolved oxygen concentration in water (Figs.7 and 9). The 90% response times of sensor B were as short as about I min and 2 min for increasing and decreasing oxygen partial pressure, respectively (Fig.8). Finally, the outer cell of sensor B was covered with antimony(V) oxide as a gasdiffusion layer (sensor C). It was found that the short-circuit current of sensor C could vary linearly with oxygen partial pressure (Fig.10(b)), with a 90% response time of about 3 min at room temperature (Fig.11).