Cobalt-based solid reference-electrode usable in zirconia-based sensors for detection of oxygen or volatile organic compounds

Abstract

The performance of oxide-based electrode formed on yttria-stabilized zirconia (YSZ) was evaluated as a solid reference-electrode (RE). Among the various electrodes examined, the Co3O4-based electrode which was formed by applying Co3O4 on the surface of a YSZ tube and then sintered at 1400°C for 9h, was found to give insensitive response to 0.05–21vol.% O2 and negligible responses to various gases (CO, NO, NO2, C3H6, C3H8, NH3, CH4, H2; 100ppm each) at the operational temperatures below 500°C. EDX and XRD analysis confirmed that Co ion from the Co3O4 layer penetrated to a YSZ substrate and formed a solid solution in YSZ. This seems to enable to attain the ability of the above-mentioned gas insensitivity of the Co3O4-based electrode formed on YSZ. The present Co3O4-based electrode (RE) was combined with Pt sensing-electrode (SE) (or NiO-SE), in order to fabricate a YSZ-based O2 sensor (or a volatile organic compounds (VOCs) sensor). The sensing characteristics of the obtained O2 sensor were comparable with those of a conventional O2 sensor using Pt-SE and Pt/air-RE. In this case, the number (n) of electrons involving in the electrochemical reaction of O2 was calculated as 4.1, which was almost same as the theoretical value (n=4.0). In addition, the fabricated VOCs sensor gave relatively good sensing characteristics even to 10ppb level of toluene (C7H8).