Surface Conversion of ZnO Tetrapods Produces Pinhole-Free ZIF-8 Layers for Selective and Sensitive H₂ Sensing Even in Pure Methane

Abstract

As the necessary transition to a supply of renewable energy moves forward rapidly, hydrogen (H2) becomes increasingly important as a green chemical energy carrier. The manifold applications associated with the use of hydrogen in the energy sector require sensor materials that can efficiently detect H2 in small quantities and in gas mixtures. As a possible candidate, we here present a metal–organic framework (MOF, namely ZIF-8) functionalized metal-oxide gas sensor (MOS, namely ZnO). The gas sensor is based on single-crystalline tetrapodal ZnO (t-ZnO) microparticles, which are coated with a thin layer of ZIF-8 ([Zn(C4H5N2)2]) by a ZnO conversion reaction to obtain t-ZnO@ZIF-8 (core@shell) composites. The vapor-phase synthesis enables ZIF-8 thickness control as shown by powder X-ray diffraction, thermogravimetric analysis, and N2 sorption measurements. Gas-sensing measurements of a single microrod of t-ZnO@ZIF-8 composite demonstrate the synergistic benefits of both MOS sensors and MOFs, resulting in an outstanding high selectivity, sensitivity (S ≅ 546), and response times (1–2 s) to 100 ppm H2 in the air at a low operation temperature of 100 °C. Under these conditions, no response to acetone, n-butanol, methane, ethanol, ammonia, 2-propanol, and carbon dioxide was observed. Thereby, the sensor is able to reliably detect H2 in mixtures with air and even methane, with the latter being highly important for determining the H2 dilution level in natural gas pipelines, which is of great importance to the energy sector.

Porous materials as effective chemiresistive gas sensors

“…In this work, Poschmann et al pointed out the use of ZnO nanoparticles in polycrystalline powder form and the conductivity hindrance effect of the ZnO–MOF–ZnO sequenced sensing material morphology. 228 Thus, they used the tetrapodal single-crystalline ZnO microparticles to avoid this undesired conductivity reduction. The ZIF-8 layer over the single-crystalline ZnO microparticles provides excellent selectivity towards the H 2 molecules, even in the presence of optimum methane concentration.…”

Solution-processable Ni3(HITP)2/MXene heterostructures for ppb-level gas detection

“…Significant advancements have been made so far toward the fabrication of MOF-based chemiresistive sensors with salient sensing performance towards a series of analytes. 12–21 For example, Zhang et al demonstrated excellent selectivity of sensors based on ZnO@ZIF-8 core–shell structures toward H 2 prepared using homogeneous precipitation and screen-printing techniques. 13 Similarly, Stock et al obtained ZnO@ZIF-8 composites with outstanding selectivity toward H 2 through ZnO transformation.…”

“…13 Similarly, Stock et al obtained ZnO@ZIF-8 composites with outstanding selectivity toward H 2 through ZnO transformation. 14 Additionally, Long et al prepared ZnO@ZIF-8 core–shell nanorod films, while Jung et al developed PMMA/ZIF-8 bilayers as molecular sieving layer with strong resistance to CO interference in H 2 detection. 15,16 Furthermore, Mao et al fabricated flexible field-effect transistor (FET) sensors based on the in situ growth of Ni 3 (HHTP) 2 , which exhibited high sensitivity to NO 2 at room temperature (with a detection limit of 56 ppb) and excellent selectivity.…”