Rare earth oxide sensors for ethanol analysis

Rare earth oxides and tin oxide for ethanol analysis in air are investigate d using AC impedance and DC resistance methods. It is found that the unprom oted rare earth oxide sensors give a significantly better sensitivity to et hanol than Pd/SnO2 sensors prepared by an incipient wetness method. This is attributed to their adsorbed oxygen species of strong basicity whereupon o xidative dehydrogenation of ethanol is effectively carried out. It is inter esting to note that the praseodymium oxide shows an entirely different sens ing mechanism amongst all of the rare earth oxides tested. Lattice oxygen o f the non-stoichiometric PrOx is involved in oxidising ethanol in air at 15 0-400 degrees C. This results in the destruction of their electron hopping sites in the mixed Pr4+ and Pr3+ lattice leading to an increase in the elec trical resistance of the material. The resistivity of this new type of oxid e sensor increases in proportion to the ethanol concentration in air and re covers to the initial value upon removal of ethanol. (C) 1998 Elsevier Scie nce S.A. All rights reserved.