Gas sensing behavior of p-NiO/n-ZnO composite nanofibers depending on varying p-NiO content: Selectivity and humidity-independence for oxidizing and reducing gas molecules

In this work, we fabricated gas sensors based on p-type NiO/n-type ZnO composite nanofibers (NFs), which could selectively detect oxidizing and reducing gas molecules. The p-type NiO/n-type ZnO composite NFs with both hetero- and homojunctions were successfully synthesized, and their sensing performances for oxidizing and reducing gases were systematically investigated with different composition ratios of p-type NiO and n-type ZnO. Interestingly, for oxidizing and reducing gases, the 0.5NiO-0.5ZnO NFs (nominal composition) exhibited an excellent gas response to oxidizing gases such as NO₂ and SO₂, whereas the 0.8NiO-0.2ZnO NFs (nominal composition) showed good selectivity for reducing gases such as C₃H₆O, C₂H₅OH, and NH₃. In addition, we also examined the NO₂ and CO sensing performance under a humid atmosphere to confirm the role of the NiO component, which possesses high affinity for water molecules, in p-type NiO/n-type ZnO composite NFs. We discussed the correlation between variations in composition and sensing performances with respect to gas sensing behavior, selectivity, and humidity effect for oxidizing and reducing gases. The results reveal that we successfully imparted selectivity for oxidizing and reducing gas molecules to the p-type NiO/n-type ZnO composite NFs by adjusting the composition ratio of NiO/ZnO.