Solid-state potentiometric gas sensors—a supplement

Potentiometric in situ gas probes with solid electrolytes were described for the first time 50 years ago. It is the intention of the present communication to give some additions on oxygen sensors in reducing gases which have been neglected in a recent review (J Solid State Electrochem, 13:3, 2009). Today, the most frequently used solid electrolyte gas sensors are the lambda probes. In their electrodes is a very quick change between gas phases with excess of oxygen and excess of components of reducing gases. Changes in the interpretation of the mechanism of the interaction between gas and solid electrolyte in the gas sensors are discussed. At low temperatures, mixed potentials appear which have to be expected at oxygen electrodes also with air and technical oxygen, if these gases are not cleaned particularly. Among the CO2 sensors, the system with the reference electrode SiO2, Na2Si2O5 on ß-alumina must be mentioned. This system has special advantages and in the commercially available device it reaches excellent long-term stability. A report about long-term measurements of SO2 traces in air is worth mentioning. For measurements of SO2 in industrial gases, Westinghouse has offered a complicated system in the 1980s.