A new type of oxygen sensor using the electrochemical oxygen pump of a zirconia electrolyte and the artificial oxygen diffusion overpotential behavior has been investigated from the theoretical and practical viewpoints of the "gas polarography," the concept of which is proposed in this paper. This new oxygen sensor has excellent oxygen sensing characteristics analogous to polarography. As a result of the artificial oxygen diffusion overpotential at the cathode, the reproducible limiting current relating to the oxygen concentration was observed over a wide oxygen concentration range up to 95% and a temperature range of 400~176 in O2-inert gas mixtures. In this paper, the factors influencing the limiting current in the normal diffusion region, that is, the oxygen molar fraction, gaseous diffusion coefficients, the temperature, the pressure, and the two geometric quantities (area and length) of the gas diffusion hole are theoretically considered.

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Output characteristics of a gas-polarographic oxygen sensor using a zirconia electrolyte have been investigated at 450°C and low pressures (∼1 mmHg) in O2-N2 gas mixtures with the aim of clarifying those in the Knudsen diffusion region. The limiting current obtained at 1 mmHg of the total pressure increased linearly with the oxygen concentration up to 100% in the ambient atmosphere as expected from the theoretical consideration on the output characteristics of the sensor in the Knudsen diffusion region.

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