Role of heterogeneous catalysis in the gas-sensing selectivity of high-temperature mixed potential sensors

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, C3H6, and C3H8 concentration using gas chromatography shows that the observed preferential sensitivity of a LaCrO3//YSZ//Pt bulk mixed potential sensor towards C3H8 is largely due to heterogeneous catalysis of the C3H6 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 C3H6 and C3H8. Although a similar amount of heterogeneous catalytic oxidation of CO takes place, the LaCrO3//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% O2 / 12% CO2 / N2 and at temperatures between 550 and 600 C