Poisoning mechanisms of Mn-containing additives on the performance of TiO2 based lambda oxygen sensor

Mn-containing additives, such as methylcyclopentadienyl manganese tricarbonyl (MMT), are usually used to improve the octane value of unleaded gasoline. Several studies have reported the adverse effects of MMT on oxygen sensors. However, the failure mechanisms of the oxygen sensor are seldom discussed. TiO2 has been widely used as oxygen lambda sensor to control the air-to-fuel ratio (A/F) in vehicles. In this work, TiO2 based lambda sensors were fabricated by thick film technology and then were directly poisoned by MMT. Their dynamic response characteristics were studied in comparison with pure TiO2 sensors. The results showed that the dynamic response properties of TiO2 lambda sensor were deteriorated sharply by MMT. XRD, SEM, EDS and XPS were used to analyze the phase structure, morphology and surface chemistry state of TiO2 sensing film poisoned by MMT. Finally, a barrier model and a resistance model were proposed to discuss the deterioration mechanisms.