Au-oxide composites as HC-sensitive electrode material for mixed potential gas sensors

In potentiometric zirconia-based gas sensors, gold electrodes show a high sensitivity for hydrocarbons (HC) when the measurements take place in nonequilibrated oxygen containing gas mixtures at temperatures < 700 degreesC. That behaviour explained by mixed potential theory is not stable and depends strongly on preparation and particularly on measuring conditions. To clarify the correlation between the potential behaviour of electrodes and their catalytic activity for the hydrocarbon combustion, we investigated composite electrodes Au-oxide/YSZ with Ga2O3, Y2O3, Al2O3, ZrO2, In2O3 and Nb2O5 as oxides and 70 mass percent gold in C3H6-O-2 gas mixtures using a platinum air reference electrode. Gold composite electrodes using Nb2O5, Ga2O3, In2O3 as oxides show, as compared with pure gold, an enhanced propylene sensitivity and a time-independent characteristic at high concentrations of C3H6. Gold composite electrodes with Y2O3, Al2O3, ZrO2 tend to the equilibrium behaviour, The catalytic activity of the Au-composites for the HC combustion correlates very well with the cell voltage response. (C) 2002 Elsevier Science B.V. All rights reserved.