Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional (1D) nanostructures. The hydrogen sensing mechanism of SMO nanostructures and some critical issues are discussed. Doping, noble metal-decoration, heterojunctions and size reduction have been investigated and proved to be effective methods for improving the sensing performance of SMO thin films and 1D nanostructures. The effect on the hydrogen response of SMO thin films and 1D nanostructures of grain boundary and crystal orientation, as well as the sensor architecture, including electrode size and nanojunctions have also been studied. Finally, we also discuss some challenges for the future applications of SMO nanostructured hydrogen sensors.

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[001]-Oriented α-MoO3 nanoribbons were synthesized via hydrothermal method at temperature from 120 to 200 °C and following assembled a membrane on interdigital electrodes to form sensors. The sensitivity, response speed, and recovery speed of the sensor improve with the increasing hydrothermal temperature. Among them, the sample obtained at 200 °C exhibits a room-temperature response time of 14.1 s toward 1000 ppm of H2. The nanoribbons also show good selectivity against CO, ethanol, and acetone, as well as high sensitivity to H2 with a concentration as low as 500 ppb. The hydrogen sensing behavior is dependent on the redox reaction between the H2 and chemisorbed oxygen species. Higher hydrothermal temperature creates larger specific surface area and higher Mo(5+) content, leading to increased chemisorbed oxygen species on the nanoribbon surface.

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Pb Ti O 3 nanowires have been successfully fabricated by a hydrothermal method at 200°C. X-ray diffraction result shows that the PbTiO3 nanowires have a tetragonal perovskite structure without any other impurity phase. Scanning electron microscopy and transmission electron microscopy investigations exhibit that the as-prepared samples are made up of large quantity nanowires with diameters of about 10–20nm and lengths reaching up to 3μm and single crystalline in nature. Photoluminescence study at room temperature for wavelength between 400 and 650nm reveals a strong blue-green emission band peaking at ca. 471.4nm (2.63eV). Raman spectroscopy study of the nanowires at room temperature demonstrates that the lifetime of the phonons is shorter compare to that of bulk materials.