A review of zirconia oxygen, NOx, and mixed potential gas sensors – History and current trends

Abstract

Zirconia-based electrochemical sensors have revolutionized oxygen monitoring and combustion control. These robust, solid-state devices are found in virtually every internal combustion engine today providing feedback information for tight air to fuel ratio control thus minimizing unwanted emissions and improving engine efficiency. Variations on the sensor design and operational mode enable the measurement of nitrogen oxides to part per million levels, providing control information for exhaust after-treatment systems. Emerging designs include the development of "gas analyzers on a chip" capable of monitoring oxygen, carbon monoxide, nitrogen oxides, ammonia and hydrocarbons. • Zirconia based electrochemical gas sensors can detect wide variety of pollutants. • Potentiometric, amperometric, impedance-based, and pulsed polarization methods are reviewed. • Modeling of sensor behavior can predict sensor response. • Machine learning techniques can be applied for sensor signal decoding.