A micron-scale bilayer sensor was fabricated in situ by electrohydrodynamic jet printing for detecting H 2 gas with highly selectivity, sensitivity and stability. The sensor consisted of a Pt loaded mesocellular silica foam (Pt-MCF) catalytic filter layer, and a ZnO/SnO 2 /Au (ZSA) sensing layer. Benefiting from the selective catalytic oxidation for CO in the catalytic filter layer, the cross-interference of CO on this sensor was reduced from 58 % to 15 %. The sensor also demonstrated a satisfactory selectivity to H 2 in interfering gases of CO 2 and CH 4 due to its high specific response to H 2 . In the ZSA sensing layer, the n-n heterojunction (ZnO-SnO 2 ) and abundant active sites on the Undaria pinnitafida -like curved nanosheet structure effectively enhanced the response of H 2 by 6.7 times. The sensors exhibited a wide H 2 dynamic range of 0.5–500 ppm with low detection limit of 94 ppb. The response/recovery time to 50 ppm H 2 was 24 s/35 s. The sensor also showed good long-term stability in 28-day response-repeatability measurement (RSD=5.3 %) and good anti-humidity.
NO 2 is one of the most important air pollutant gases for the environment and human health. H 2 is seen as the next generation of clean energy to promote sustainable development. However, sensitive detection of NO 2 at room temperature is still a major challenge, and reliable H 2 sensors are also scarce. Metal oxide semiconductor (MOS) gas sensors are advantageous for detecting gas. Hence, we synthesized the unique hexahedral hollow mesoporous In 2 O 3 (h-In 2 O 3 ) derived from MIL-68 (In). The formation process and properties of h-In 2 O 3 were analyzed. The surface of h-In 2 O 3 is rich in hydroxyl groups , which are active sites for NO 2 adsorption at room temperature. Increasing working temperature up to 160 °C enables effective sensing reaction with H 2 . Based on different temperature-dependent gas sensing mechanisms, the h-In 2 O 3 sensor exhibits ultrasensitive response values of 400 towards 100 ppb NO 2 at room temperature (24 °C) and of 17.99 towards 10 ppm H 2 at 160 °C. In addition, the h-In 2 O 3 sensor exhibits reliable linear response, low theoretical detection limit of 1.8 ppt and 23 ppb for NO 2 and H 2 , excellent selectivity, repeatability and long-term stability. The synergistic effect of the unique structure, larger specific surface area , and abundant adsorbed oxygen plus oxygen vacancy contribute to the excellent gas sensing performance of the h-In 2 O 3 sensor. This study provides a promising strategy for the development of bifunctional gas sensors.
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