Degradation mechanism of TiO2 based lambda oxygen sensor poisoned by phosphorus

TiO2 is one of the most popular materials used as air/fuel ratio (A/F) oxygen lambda sensor for automobiles, because of its excellent gas sensing properties. As is well known, the composition of gasoline is very complex and trace amounts of phosphorus-containing additives are present in many kinds of gasoline. Many studies have shown that a large amount of phosphorus containing particles is loaded on the surface of the failed oxygen sensor. However, few studies have focused on the effects of phosphorus on the TiO2 sensing film. In this work, pure TiO2 and P2O5 contaminated TiO2 oxygen lambda sensor were prepared to discuss the effects of phosphorus on TiO2 sensing film. The results showed that the transient response of the sensor is significantly affected when TiO2 is poisoned by P2O5. XRD, SEM, EDS and XPS were used to analyze the phase structure, morphology and surface chemistry state of TiO2 sensing film poisoned by P2O5. It is found that the TiO2 surface was coated by phosphate radical, resulting in a barrier layer on the grain surface which blocks the transfer of electrons to O2 molecule.