A concept of chemical potential pumping effect of nonstoichiometric oxides and the NOx sensing mechanism of the Perovskite-type la 0.5Sr0.5FeO3

Abstract

A concept of chemical potential pumping effect was introduced to describe the NOx sensing mechanism of oxide catalysts with high electronic conductivity and large carrier density. When NOx gas in a gas-stream decomposed on the surface of the catalyst oxides continuously, the high oxygen potential released by the decomposition of NOx stationarily covered the whole surface of the oxide. Then, the bulk oxide was equilibrated with the steady-state high oxygen potential of the surface, which was much larger than that determined by the oxygen pressure of the surrounding gas-phase. This effect was confirmed by the conductivity enhancement of La2CuO 4.and La0.5Sr0.5FeO3 with NO 2 as well as nonstoichiometry variation of La0.5Sr 0.5CoO3 and EMF of galvanic cell with La 0.6Sr0.4CoO3-d. It was shown that the chemical potential pumping effect appears essentially on dense materials while the effect is hardly observed on porous material with large surface relative. On La 0.5Sr0.5FeO3 as well as on La 2CuO4, NO2 was found to decompose into NO and O2, while NO was almost inactive on these oxides.