Yttria-stabilized zirconia (YSZ) is a pure oxygen ion conductor at high temperatures and has high chemical stability, which is used in many areas, including fuel cells, oxygen sensors and insulation coatings.
By incorporating yttria into zirconia (YSZ), oxygen ion vacancies are generated to improve the conductivity of oxygen ions.
(Illustrated in Figure 1) YSZ- Unit cell structure
( J. Phys.: Condens. Matter 25, 2013, 395001)
Our company produces oxygen gas sensors mainly using 8mol% yttria-stabilized zirconia (YSZ), which is one of the best compositions for an oxygen ionic conductor.
(illustrated in Figure 2) Structure of Zirconian Oxygen Sensors Using YSZ
As illustrated in Figure 2, a zirconia oxygen sensor has a structure with a reference electrode and a working electrode isolated from each other.
The reference electrode is exposed to the ambient atmosphere that always has an oxygen partial pressure of 21%. The sampling gas to be measured flows onto the working electrode. The sampling gas to be measured circulates through the working electrode to measure the oxygen partial pressure.
Oxygen molecules in a gaseous state fill the vacancies of oxygen ions on the surface of YSZ through the following reaction formula, and electrons are lost.
At a fixed temperature, the concentration of each electrochemical species can be expressed as the following formula by the mass action law.
The concentration of the oxygen ion vacancy is decided by the doping concentration of Yttria, therefore the concentration of electrons is proportional to the oxygen partial pressure.
Hence, the difference in oxygen partial pressures between the reference electrode and the working electrode results in an electrical potential difference between the two electrodes on the YSZ.
The potential difference between the two electrodes is defined by the Nernst equation.
Since the oxygen partial pressure at the reference electrode is known, Measuring the potential difference between the two electrodes allows the calculation of the oxygen partial pressure in the sample gas.
Because of its excellent chemical stability and corrosion resistance, the zirconia oxygen sensor can work stably under various gas conditions, so it can be widely used in various application fields to measure the oxygen partial pressure in any practical range.