Figure 1: Schematic structure of a potentiometric planar oxygen
sensor. (A) Measuring atmosphere. (B) Porous protective layer.
This layer is optional as it prevents from electrode degradation
and sometimes it improves the sensor response due to gas species
diffusion. (C) Measuring electrode, catalytically active,
generally made of platinum. (D) O2- ion-conductive ceramic
electrolyte. The most used electrolyte is Y2O3-doped ZrO2 (YSZ).
(E) Reference electrode, in contact with (F) Air reference
atmosphere. Some sensors have been occasionally described
without a reference atmosphere. Also, a heating element (a
dissipative low resistance) is optionally put in front of this
sensor structure to achieve stable, high enough temperatures.