Self-heated HTCC-based ceramic disc for mixed potential sensors and for direct conversion sensors for automotive catalysts

Solid electrolyte gas sensors following the mixed potential sensing principle are usually operated at several hundred °C. They are often characterized using half-cell setups where one side of the sensor faces a reference gas atmosphere whereas the other side faces the gas mixture to be analyzed. Since two gas compartments are compared, a high temperature sealing is needed. Typically, such setups require indirect heating, and often, the manufacturing process is complicated and the dismantling of sensor and sealing is only possible by destroying it. To overcome these and other drawbacks of the half-cell setup, a self-heatable, stand-alone ceramic sensor device is developed in this work. We choose high temperature co-firing ceramics technology for the sensor design that bases on a self-heated yttria-stabilized zirconia disc that is hot enough for sensing in the central region and cold enough at the outer radius for contacting and plastic sealing. This work shows how problems that occurred due to the high thermal stress were overcome by employing finite element simulations. After developing and manufacturing the novel device, it is demonstrated that the sensor is capable to compare two gas mixtures electrochemically. For that purpose, the device was used to compare the gas composition up- and downstream of an oxidation catalyst. The sensor signal response correlates well with a theoretically derived dependence on the catalyst conversion.