Developing hydrogen sensors with parts per billion-level detection limits, high response, and high stability is crucial for ensuring safety across various industries (e.g., hydrogen fuel cells, chemical manufacturing, and aerospace). Despite extensive research on parts per billion-level detection, it still struggles to meet stringent requirements. Here, high performance and ppb-level H2 sensing have been developed with palladium-doped iron oxide nanotubes (Pd@Fe2O3 NTs), which have been prepared by FeCl3·6H2O, PdCl2, and PVP electrospinning and air calcination techniques. Various characterization techniques (FESEM, TEM, XRD, and so forth) were used to prove that the nanotube structure was successfully prepared, and the doping of Pd nanoparticles was realized. The experiments show that palladium doping can significantly improve the gas response of iron oxide nanotubes. Specifically, 0.59 wt % Pd@Fe2O3 NTs have high response (Ra/Rg = 41,000), high selectivity, and excellent repeatability for 200 ppm hydrogen at 300 °C. Notably, there was still a significant response at a low detection limit (LOD) of 50 ppb (Ra/Rg = 16.8). This excellent hydrogen sensing performance may be attributed to the high surface area of the nanotubes, the p–n heterojunction of PdO/Fe2O3, which allows more oxygen to be adsorbed on the surface, and the catalytic action of Pd nanoparticles, which promotes the reaction of hydrogen with surface-adsorbed oxygen.
Constructing heterostructures is an effective strategy to improve the performance of semiconductor metal oxide . The heterostructure exhibits strong interaction between tightly packed interfaces, showing better performance than a single structure. Therefore, indium sulfide (In 2 S 3 )/tungsten oxide (WO 3 ) composites were synthesized with heterojunction by a simple hydrothermal method to enhance the gas sensing performance of WO 3 . The WO 3 and In 2 S 3 exist in the form of nanoparticles . Then the gas sensing test of the material was carried out, by exploring the performance of WO 3 based on doping different amounts of In 2 S 3 , the response of WO 3 based on 3 wt% In 2 S 3 to 10 parts per million (ppm) nitrogen dioxide (NO 2 ) is 170.1 at the optimum operating temperature of 170 °C. Compared with pure WO 3 , the response is enhanced by seven times. Besides, the detection limit of the sample is low. The minimum detection concentration of NO 2 can reach 20 parts per billion (ppb). The reason for the improved performance can be attributed to the wider electron depletion layer or hole accumulation layer formed by the heterojunction for electron transfer . Finally, a convenient wearable NO 2 Real-time Detection System is designed to detect different concentrations of NO 2 in the factory, which provides an effective alarm mean for the excessive emission of industrial waste gas in the factory environment.
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