High-Performance Nanowire Hydrogen Sensors by Exploiting the Synergistic Effect of Pd Nanoparticles and Metal–Organic Framework Membranes

Abstract

Herein, we report the fabrication of hydrogen gas sensors with enhanced sensitivity and excellent selectivity. The sensor device is based on the strategic combination of ZnO nanowires (NWs) decorated with palladium nanoparticles (Pd NPs) and a molecular sieve metal-organic framework (MOF) nanomembrane (ZIF-8). The Pd NPs permit the sensors to reach maximal signal responses, whereas the ZIF-8 overcoat enables for an excellent selectivity. Three steps were employed for the fabrication: (i) coating of a miniaturized sensor with vapor-grown ZnO NWs, (ii) decoration of these NWs with Pd NPs by atomic layer deposition, and (iii) partial solvothermal conversion of the tuned NWs surface to ZIF-8 nanomembrane. The microstructure and composition investigations of the ZIF-8/Pd/ZnO nanostructured materials confirmed the presence of both metallic Pd NPs and uniform ZIF-8 thin membrane layer. The integration of these nanomaterials within a miniaturized sensor device enabled the assessment of their performance for H detection at concentrations as low as 10 ppm in the presence of various gases such as CH, CH, CHOH, and CHCOCH. Remarkably high-response signals of 3.2, 4.7, and 6.7 ( R/ R) have been measured for H detection at only 10, 30, and 50 ppm, whereas no noticeable response toward other tested gases was detected, thus confirming the excellent H selectivity obtained with such a sensor design. The results obtained showed that the performance of gas sensors toward H gas can be greatly increased by both the addition of Pd NPs and the use of ZIF-8 coating, acting as a molecular sieve membrane. Furthermore, the presented strategy could be extended toward the sensing of other species by a judicious choice of both the metallic NPs and MOF materials with tuned properties for specific molecule detection, thus opening a new avenue for the preparation of highly selective sensing devices.

Well-dispersed Pd nanoparticles on porous ZnO nanoplates via surface ion exchange for chlorobenzene-selective sensor

“…[15][16][17] Recently, the sensors based on ZnO nanowires decorated with Pd nanoparticles have also been reported, which obtain high selectivity and sensitivity. 18,19 The poor response and low sensing selectivity of metal-oxide gas sensors towards chlorobenzene are caused by the chemically inert molecular structure of chlorobenzene. 20 Pt and Pd nanoparticles are considered to have better sensitization activity; however, Pd is more economical than Pt.…”

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“…The vacuum chamber was set at a temperature of 220 • C, and the lines were heated at 100 • C in order to prevent condensation. Further details about both this deposition protocol and the associated ALD reactor can be found elsewhere [25,26].…”

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