Electrochemical abatement of pollutants NO[sub x] and SO[sub x] in combustion exhaust gases employing a solid-oxide electrolyte

Abstract

The role of oxygen vacancies in the conductivity of ESB was studied using such solidstate techniques as differential thermal analysis and x-ray diffraction. A change in the slope of conductivity vs. reciprocal temperature, at [approximately]600[degrees]C, indicates two different conductivity regions. The above techniques were used to show that the change in slope is due to an order-disorder transition of the oxygen sublattice. At high temperatures, the oxygen sublattice is disordered resulting in a high mobility of oxygen vacancies and a low apparent activation energy. At low temperatures the oxygen sublattice tends to order, with the vacancies aligning in (111) planes. The higher activation energy in this temperature regime is than due to the extra energy required to free a vacancy from the ordered state. Furthermore, a reversible aging phenomenon in the conductivity of ESB was observed. For ESB annealed in this lower temperature region, the conductivity was observed to decay with time as the oxygen sublattice ordered. Heating above transition point will completely reverse this process by disordering the oxygen sublattice, and returning the conductivity to its initial value.