Humidity-independent gas sensor based on Pt/SnO2/NiO with advanced CO sensing capabilities

Aimed at realizing the sensors capable of functioning effectively in high-humidity environments, the Pt/SnO₂/NiO ternary composite materials featuring noble metal and p-n heterojunction structures was synthesized. The dispersion of SnO₂ and Pt nanoparticles on NiO nanosheets was found to be excellent, resulting in a nearly twofold increase (99.45 m²g^-1 of Pt/SnO₂/NiO) in specific surface area compared to pure NiO materials (51.977 m²g^-1). The CO sensitivity tests revealed that, in contrast to pure NiO sensors (with an optimal operating temperature of 290°C), Pt/SnO₂/NiO ternary composites exhibited an optimal operating temperature (OOT) of 270℃, a decrease of 20℃ for CO detection at a relative humidity of 22%. At this OOT, Pt/SnO₂/NiO sensors consistently displayed high responsiveness (2.5 times higher than that of the pure NiO sensor), good selectivity, and rapid response-recovery times (the recovery time is reduced by nearly half compared to that of the pure NiO sensor). Furthermore, the sensors' responses to CO under different humidity conditions (from 22% to 91%) at 270℃ were investigated. The results demonstrated that Pt/SnO₂/NiO sensors exhibited minimal variation in their response to CO at a range of relative humidity levels (41.5% at 91%, 39.5% at 22%, respectively). These results highlight that the enhancement of CO gas sensitivity in the sensors primarily results from the high catalytic activity of noble metal Pt and the p-n heterojunction interaction.