Hydrogen (H₂) is attracting attention as a renewable energy source in various fields. However, H₂ has a potential danger that it can easily cause a backfire or explosion owing to minor external factors. Therefore, H₂ gas monitoring is significant, particularly near the lower explosive limit. Herein, tin dioxide (SnO₂) thin films were annealed at different times. The as-obtained thin films were used as sensing materials for H₂ gas. Here, the performance of the SnO₂ thin film sensor was studied to understand the effect of annealing and operating temperature conditions of gas sensors to further improve their performance. The gas sensing properties exhibited by the 3-h annealed SnO₂ thin film showed the highest response compared to the unannealed SnO₂ thin film by approximately 1.5 times. The as-deposited SnO₂ thin film showed a high response and fast response time to 5% H₂ gas at 300 °C of 257.34% and 3 s, respectively.

The gasochromism of WO₃, wherein the color of the material changes according to the reaction of gas, can immediately allow for the determination of the presence of hydrogen by the naked eye. We have also developed a hybrid hydrogen sensor for WO₃, a metal oxide, that can simultaneously utilize its gasochromic response and resistance to hydrogen. Because the proposed sensor has a transparent electrode on a glass substrate, it is a structure that can not only reveal the change in resistance but also more clearly illustrate the gasochromic response. A hybrid sensing demonstration in a hydrogen leak environment was successfully performed to verify a sensor that was capable of utilizing the resistive and gasochromic response of WO₃.

This work presents the design and evaluation of cerium and zinc oxide-incorporated indium oxide (Ce/ZnO-In₂O₃) nanocube composites synthesized via a hydrothermal process for advanced ethanol gas sensing. The incorporation of Ce and ZnO effectively modified the surface chemistry and electronic structure of In₂O₃ without causing significant morphological degradation. Compared with pristine In₂O₃, the Ce/ZnO-In₂O₃ sensor exhibited a significantly enhanced response of 33.2 toward 100 ppm ethanol at 300 °C, corresponding to an 8.7-fold improvement, along with a low detection limit of 0.8 ppm. In addition, the composite sensor demonstrated stable and reversible sensing behavior, excellent repeatability over 100 cycles, and long-term operational stability. Notably, improved humidity tolerance was achieved, with approximately 77% of the initial response retained at 80% relative humidity. The enhanced sensing performance is attributed to the combined effects of heterojunction formation between ZnO and In₂O₃ and Ce-induced lattice distortion, which promote oxygen adsorption and facilitate charge transfer during gas reactions. Principal component analysis (PCA) further confirmed the improved discrimination of ethanol against interfering gases. These results underscore the synergistic effects of Ce and ZnO incorporation in tailoring electronic structures and surface chemistry, thereby emphasizing the potential of this strategy for reliable ethanol detection in environmental and industrial applications.