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

Abstract

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 °C. 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 Ga 2O 3, Y 2O 3, Al 2O 3, ZrO 2, In 2O 3 and Nb 2O 5 as oxides and 70 mass percent gold in C 3H 6–O 2 gas mixtures using a platinum air reference electrode. Gold composite electrodes using Nb 2O 5, Ga 2O 3, In 2O 3 as oxides show, as compared with pure gold, an enhanced propylene sensitivity and a time-independent characteristic at high concentrations of C 3H 6. Gold composite electrodes with Y 2O 3, Al 2O 3, ZrO 2 tend to the equilibrium behaviour. The catalytic activity of the Au-composites for the HC combustion correlates very well with the cell voltage response.