In Situ Growth of NiO@SnO₂ Hierarchical Nanostructures for High Performance H₂S Sensing

Heterostructured metal oxides with large specific surface area are crucial for constructing gas sensors with high performance. However, using slurry-coating and screen-printing methods to fabricate gas sensors cannot result in high uniformity and reproducibility of the sensors. Here, NiO nanowalls decorated by SnO₂ nanoneedles (NiO@SnO₂) were in situ grown on ceramic microchips via a chemical bath deposition method to detect H₂S instead of print-coating and slurry-coating methods. The morphologies and compositions of the NiO@SnO₂ hierarchical nanostructures (HNSs) were well tuned by varying the growth time of the NiO@SnO₂ HNSs to optimize the sensing performance. The response of the NiO@SnO₂ HNSs (2 h) to 1 ppm of H₂S was over 23-fold higher than that of the pure NiO nanowalls and 17-fold higher than that of the pure SnO₂ nanosheets. This dramatic enhancement is attributed to the large surface area of the NiO@SnO₂ HNSs and the p-n heterojunction at the heterointerface of SnO₂ and NiO. The variation in the depletion layers (W_SnO2 and W_NiO) at the heterointerface of SnO₂ and NiO greatly depends on the properties of the target gases (e.g., electron-withdrawing property (NO₂) or electron-donating property (H₂S)).