Enhanced CO sensing characteristics of hierarchical and hollow In2O3 microspheres

Hierarchical and hollow In2O3 microspheres were prepared by a solvothermal self-assembly reaction and their CO sensing characteristics were compared to those of an agglomerated counterpart. Upon exposure to 10–50 ppm CO at 400 °C, the gas responses (Ra/Rg; Ra: resistance in air, Rg: resistance in gas) of the hierarchical and hollow structures were 1.6–2.7 times higher than that of the agglomerated sample. In addition, their 90% responses and recovery speeds were 23 times and 7.7 times higher, respectively. Their significantly improved gas responses and sensing/recovery kinetics were concluded to be related to the nanoporous and well-aligned nanostructures, which allow effective and rapid gas diffusion toward the sensing surfaces.