Amperometric sensors w ith yttria-stabilized zirconia (YSZ) discs and YSZ cylinders were made with platinum electrodes applied on the YSZ disc, which served as working (inside) and counter (outside) electrodes, and a platinum wire electrode positioned along the circumference o f the disc. Two sets o f platinum electrodes were applied on the YSZ cylinder, one inside and the other outside. The YSZ cylinder was attached to the YSZ disc using a sealing glass. A YSZ disc with a tiny diffusion hole

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... s glass-sealed on the other end o f the YSZ cylinder. The amperometric sensor was tested at 800°C in air over an applied DC voltage range from zero to 2.5 V. The measured current over a voltage range from ~0.4 to -1 .6 V exhibited a plateau. For applied voltage >1.7 V, the measured current increased, with a rapid increase for applied voltage >1,9 V. This rapid rise is consistent with the development o f nonstoichiometry or the occurrence o f YSZ electrolyte decomposition. The voltage between the reference and the working electrodes was measured. Based on this information, the cathodic activity o f the platinum working electrode was estimated. Implications concerning the use o f the three electrode system for the study o f electrode polarization are discussed.