The Role of Heterogeneous Catalysis in the Gas-Sensing Selectivity of High-Temperature Mixed Potential Sensors

摘要

The sensitivity of a mixed potential electrochemical sensor is determined by the concentration of the analyte gas at the gas/electrode/electrolyte interface. These concentrations, along with the kinetic properties of the three-phase interface and oxygen partial pressure, establish the mixed potential generated by the device. The selectivity of mixed potential sensors is therefore strongly influenced by the heterogeneous catalytic properties of the surfaces that closely surround the sensor including: the metal oxide electrode, solid electrolyte, other components of the sensor body, and the sensor enclosure. Analysis of the change in CO, C_3H_6, and C_3H_8 concentration using gas chromatography shows that the observed preferential sensitivity of a LaCrO_3//YSZ//Pt bulk mixed potential sensor towards C_3H_8 is largely due to heterogeneous catalysis of the C_3H_6 on the sensor body, which in this work, is YSZ. By blocking YSZ heterogeneous catalysis by using a coating of thick Au, the sensor exhibits nearly identical sensitivity to both C_3H_6 and C_3H_8. Although a similar amount of heterogeneous catalytic oxidation of CO takes place, the LaCrO_3//YSZ//Pt sensor exhibits only a small response to CO and this therefore may be associated with the electrode kinetics and electrocatalytic properties of the sensor interface towards the electro-oxidation of the CO. Data for HC and CO selectivity will be presented at 1% O_2 / 12% CO_2 / N_2 and at temperatures between 550 and 600°C.