NO₂ sensing properties of WO₃-decorated In₂O₃ nanorods and In₂O₃-decorated WO₃ nanorods

In₂O₃ nanoparticle (NP)-decorated WO₃ nanorods (NRs) were prepared using sol-gel and hydrothermal methods. The In₂O₃ NRs and WO₃ NPs were crystalline. WO₃ NP-decorated In₂O₃ NRs were also prepared using thermal evaporation and hydrothermal methods. The NO₂ sensing performance of the In₂O₃ NP-decorated WO₃ NR sensor toward NO₂ was compared to that of the WO₃ NP-decorated In₂O₃ NR sensor. The former showed a high response to NO₂ due to a significant reduction of the conduction channel width upon exposure to NO₂. In contrast, the latter showed a far less pronounced response due to limited reduction of the conduction channel width upon exposure to NO₂. When the sensors were exposed to a reducing gas instead of an oxidizing gas (NO₂), the situation was reversed, i.e., the WO₃ NP-decorated In₂O₃ NR exhibited a stronger response to the reducing gas than the In₂O₃ NP-decorated WO₃ NR sensor. Thus, a semiconducting metal oxide (SMO) with a smaller work function must be used as the decorating material in decorated heterostructured SMO sensors for detection of oxidizing gases. The In₂O₃ NP-decorated WO₃ NR sensor showed higher selectivity for NO₂ compared to other gases, including reducing gases and other oxidizing gases, as well as showed high sensitivity to NO₂.