Gold-Composite Electrodes for Hydrocarbon Sensors Based on YSZ Solid Electrolyte

In potentiometric zirconia based sensors gold electrodes show a high sensitivity for hydrocarbons (HC's) when the measurements are carried out in non equilibrated oxygen containing gas mixtures at temperatures < 700 degrees C. This behaviour explained by mixed potential theory is not stable and depends strongly on preparation and particularly on measuring conditions. To modify the electrode behaviour composites consisting of gold and gallium oxide were investigated. Gold pastes with different amount of Ga(2)O(3) were prepared and screen printed on YSZ pellets. After sintering at defined temperatures between 900 and 950 degrees C the cells were tested regarding the electrode behaviour in a C(3)H(6), O(2) gas mixture using a platinum air reference electrode. These composite electrodes show as compared with pure gold an enhanced sensitivity at low propylene concentrations and a time-independent characteristic at high concentrations of C(3)H(6). The optimal composition is found to be at 20 mass-% Ga(2)O(3). This electrode can be treated in reducing gases at temperatures 850 degrees C without changing its characteristics.