Development of long-life galvanic oxygen sensor

The galvanic cell-type oxygen sensor makes use of the straight line relation between the current value and the oxygen concentration obtained when the oxygen-lead cell is discharged in the oxygen diffusion rate-determining range. There are problems of life and the influence of CO{sub 2} on the alkali electrolytic solution, however, and a new sensor was developed by solving above problems. For a long life of the sensor, it is necessary that the negative electrode product PbO dissolves into the electrolytic solution and that the surface of Pb is always fresh and keeps the constant electric potential. Accordingly, by using organic acid aqueous solution, the solubility of PbO was increased and at the same time the influence of CO{sub 2} was removed. But with acidic electrolytic solution, H{sub 2} is generated from the positive electrode, so by adding lead acetate this generation of H{sub 2} was prevented. The diaphragm is the fluorine system polypro-copolymer, and the porous Au is used as the material of the positive electrode. The diaphragm and the positive electrode are integrated to avoid the thickness fluctuation of the electrolyte membrane, and to stabilize the output voltage. As the collector, porous and conductive carbon paper was applied. The result of an accelerated life experiment was from 2.5 to 12 years. The sensor's utilization rate of the electrolytic solution was from 90 to 96 percent. 3 refs., 10 figs., 1 tab.