Xie Lijuan,Li Zhong,Sun Linchao,Dong Baoxia,Fatima Qawareer,Wang Zhe,Yao Zhengjun,Haidry Azhar Ali
Titanium dioxide is considered as one of the potential candidates for high-temperature gas sensing applications due to its excellent sensitivity and stability. However, its practical use as a gas sensor under elevated conditions is limited on account of its selectivity and insufficient understanding of response conversion from n- to p-type. To this context, the present work is intended to prepare and understand the p-type response of anatase TiO2 toward H2 gas (20–1,000 ppm) at elevated temperature (500°C). Sol-gel route is adopted to facilely synthesize powders containing pure and chromium (1–10 at.%) doped TiO2 nanoparticles, which are then brushed onto substrates with already patterned inter-digitated platinum electrodes. In this work, even, the undoped TiO2 samples showed p-type gas sensing response, which then decreased with Cr doping. However, in comparison to previously reported work, the sensing characteristics of all sensors is improved. For instance, 5 at.% Cr-TiO2 showed high response (147), fast response and recovery (142/123s) time, and good selectivity to hydrogen against monoxide and methane. Despite better response values, the TiO2 based samples show instability and drift in baseline resistance; such issues were not observed for Cr-doped TiO2 samples (≥3 at.%). The powders were further analyzed by XRD, SEM, TEM, and XPS to understand the basic characteristics, p-type response and stability. Further, a plausible sensing mechanism is discussed on basis of results obtained from aforementioned techniques.
The research and development of low-power-consumption and room-temperature hydrogen sensors are of great significance for the safe application of hydrogen energy. Herein, orthorhombic Nb2O5–x nanobelts are prepared through a combined procedure of hydrothermal, ion exchange, and annealing treatment in Ar. The topological transformation process results in the formation of abundant surface defects including chemical defects such as Nb4+, oxygen vacancies, and disordered microregions, which lead to the abnormal p-type conducting and hydrogen sensing behavior. Moreover, the orthorhombic Nb2O5–x nanobelts exhibit fast and sensitive room-temperature hydrogen sensing performance, which shows greater advancement than the monoclinic, tetragonal, and hexagonal Nb2O5 one-dimensional (1D) nanostructures. The response time and lowest limit of detection of the as-fabricated room-temperature sensor decrease to 28 s and 3.5 ppm, respectively. The sensor also exhibits a highly selective hydrogen response against CO, CH4, ethanol, H2S, and NH3. The hydrogen response of the Nb2O5–x nanobelts can be attributed to the redox reaction between hydrogen and preadsorbed oxygens. The defective surface structure and the prolonged dimension of the nanobelts give rise to the highly reactive surface and the suppression of the negative nanojunction effect, which greatly improves the sensing performance. The orthorhombic lattice structure can also promote gas adsorption and diffusion behavior due to its specific catalytic and pathway effect. The results of this work can be helpful for the rational design and defect engineering of the Nb2O5-based 1D nanostructures for room-temperature hydrogen sensing applications.
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