CeO₂ nanocubes with metastable {100} facets and CeO₂ nanooctahedrons with the most stable {111} facets are herein fabricated by controlling the morphology and facets of CeO₂ nanoparticles. SnO₂ nanosheet-based assembled films coated with these CeO₂ nanocubes or CeO₂ nanooctahedrons yield {100} CeO₂ nanocubes/SnO₂ nanosheets and {111} CeO₂ nanooctahedron/SnO₂ nanosheet hybrid gas sensors, respectively. The hybrid sensors with CeO₂ nanoparticles exhibited enhanced sensing responses to numerous chemical species relative to a pristine SnO₂ nanosheet gas sensor, including acetone, hydrogen, ethanol, ammonia, acetaldehyde, and allyl mercaptan. In particular, the responses of {100} CeO₂ nanocubes/SnO₂ nanosheets and {111} CeO₂ nanooctahedron/SnO₂ nanosheet gas sensors to acetone or allyl mercaptan were 6.8 and 10.3 times higher, respectively, than that of the pristine SnO₂ nanosheet gas sensor. Furthermore, the sensor response to ammonia was 2.5 times higher than that of a commercial volatile organic compound (VOC) gas sensor (TGS2602, Figaro Engineering Inc.). The CeO₂ nanocube-based sensor with exposed metastable {100} facets promotes the adsorption and oxidation of VOCs owing to the higher surface energy of the metastable {100} facets and therefore exhibits a higher sensing performance than the CeO₂ nanooctahedron-based sensor with an exposed {111} facet. The developed sensors show excellent potential for the detection of gas markers in human breath and perspiration for disease diagnosis.

Vertically formed and well-defined SnO₂ nanosheets are easy to fabricate, involving only a single process that is performed under moderate conditions. In this study, two different sizes of a SnO₂ nanosheet were concurrently formed on a Pt interdigitated electrode chip, with interconnections between the two. As the SnO₂ nanosheets were grown over time, the interconnections became stronger. The ability of the fabricated SnO₂ nanosheets to sense H₂ gas was evaluated in terms of the variation in their resistance. The resistance of a SnO₂ nanosheet decreased with the introduction of H₂ gas and returned to its initial level after the H₂ gas was replaced with air. Also, the response–recovery behaviors were improved as a result of the growth of the SnO₂ nanosheets owing to the presence of many reaction sites and strong interconnections, which may provide multipassages for the electron transfer channel, leading to the acceleration of the reaction between the H₂ gas and SnO₂ nanosheets.