Mesoporous ceramic oxides as humidity sensors: A case study for gadolinium-doped ceria

Mesoporous materials have been studied as high performance sensing materials due to their singular microstructure and extremely high surface-to-volume ratio. However, the lack of stability of these nanostructures is assumed as one of the major drawbacks toward their application in real devices. In this work, this limitation is overcome by the synthesis of thermally stable mesoporous gadolinium doped ceria. Humidity sensors were fabricated and tested under different (i.e. humidity and temperature) conditions. The mesoporous layers were attached to the substrate at 900°C preserving mesoporous structure intact. This process at high temperature provides the layer with a mechanical strength and allows self-cleaning cycles at high temperatures if required. The humidity sensing mechanism is presented and discussed in detail by means of impedance spectroscopy. An ionic type of conduction mechanism is corroborated. Fast response and recovery, as well as very low hysteresis and no drift are observed. It was also shown that the response of the devices can be straightforwardly tuned by changing layer thickness or pore size, allowing to fulfill sensing needs of different applications. All the mentioned properties joined to the simplicity of the fabrication and the flexibility of the used fabrication route for synthesizing any other metal oxide make this kind of devices a potential group for developing high performance and fast gas sensors.