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

The performance of oxide-based electrode formed on yttria-stabilized zirconia (YSZ) was evaluated asa solid reference-electrode (RE). Among the various electrodes examined, the Co3O4-based electrodewhich was formed by applying Co3O4 on the surface of a YSZ tube and then sintered at 1400 degrees C for 9 h, was found to give insensitive response to 0.05-21 vol.% O-2 and negligible responses to various gases( CO, NO, NO2, C3H6, C3H8, NH3, CH4, H-2; 100 ppm each) at the operational temperatures below 500. C. EDX and XRD analysis confirmed that Co ion from the Co(3)O(4)layer penetrated to a YSZ substrate andformed a solid solution in YSZ. This seems to enable to attain the ability of the above-mentioned gasinsensitivity of the Co3O4-based electrode formed on YSZ. The present Co3O4-based electrode (RE) wascombined with Pt sensing-electrode (SE) (or NiO-SE), in order to fabricate a YSZ-based O-2 sensor (or avolatile organic compounds (VOCs) sensor). The sensing characteristics of the obtained O-2 sensor werecomparable with those of a conventional O-2 sensor using Pt-SE and Pt/air-RE. In this case, the number (n) of electrons involving in the electrochemical reaction of O-2 was calculated as 4.1, which was almost sameas the theoretical value (n = 4.0). In addition, the fabricated VOCs sensor gave relatively good sensingcharacteristics even to 10 ppb level of toluene (C7H8). (C) 2014 Elsevier B. V. All rights reserved.