Selectivity of HC-sensitive electrode materials for mixed potential gas sensors

Abstract

In potentiometric zirconia-based gas sensors, electrodes with medium catalytic activity show a high sensitivity for hydrocarbons (HCs) when the measurements take place in non-equilibrated oxygen containing gas mixtures at temperatures ≤800 °C. This behaviour, explained by mixed potential theory, depends strongly on preparation and particularly on measuring conditions. To learn more about the processes at the electrode surface and their influence on the potential behaviour of the electrodes, we investigated composite electrodes Au-oxide/YSZ with Ga 2O 3, In 2O 3 and Nb 2O 5 as oxides and 80 mass% Au and perovskite electrodes made of La 1− x Sr x Cr 1− y Ga y O 3− δ in N 2-diluted gas mixtures containing O 2 and different combustibles like C 3H 6, C 3H 8, CO and C 7H 8. As compared with perovskite electrodes, gold composite electrodes using Nb 2O 5 as oxide show enhanced sensitivities especially to C 7H 8. The temperature dependence of the catalytic activity for the HC combustion correlates very well with the temperature/voltage response.