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Abstract The humidity dependence of the gas‐sensing characteristics in SnO 2 ‐based sensors, one of the greatest obstacles in gas‐sensor applications, is reduced to a negligible level by NiO doping. In a dry atmosphere, undoped hierarchical SnO 2 nanostructures prepared by the self‐assembly of crystalline nanosheets show a high CO response and a rapid response speed. However, the gas response, response/recovery speeds, and resistance in air are deteriorated or changed significantly in a humid atmosphere. When hierarchical SnO 2 nanostructures are doped with 0.64–1.27 wt% NiO, all of the gas‐sensing characteristics remain similar, even after changing the atmosphere from a dry to wet one. According to diffuse‐reflectance Fourier transform IR measurements, it is found that the most of the water‐driven species are predominantly absorbed not by the SnO 2 but by the NiO, and thus the electrochemical interaction between the humidity and the SnO 2 sensor surface is totally blocked. NiO‐doped hierarchical SnO 2 sensors exhibit an exceptionally fast response speed (1.6 s), a fast recovery speed (2.8 s) and a superior gas response ( R a / R g = 2.8 at 50 ppm CO ( R a : resistance in air, R g : resistance in gas)) even in a 25% r.h. atmosphere. The doping of hierarchical SnO 2 nanostructures with NiO is a very‐promising approach to reduce the dependence of the gas‐sensing characteristics on humidity without sacrificing the high gas response, the ultrafast response and the ultrafast recovery.
Kim et al. (Fri,) studied this question.