Surface Conversion of ZnO Tetrapods Produces Pinhole-Free ZIF-8 Layers for Selective and Sensitive H(2) Sensing Even in Pure Methane

[Image: see text] As the necessary transition to a supply of renewable energy moves forward rapidly, hydrogen (H(2)) 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 H(2) 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(C(4)H(5)N(2))(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 N(2) 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 H(2) 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 H(2) in mixtures with air and even methane, with the latter being highly important for determining the H(2) dilution level in natural gas pipelines, which is of great importance to the energy sector.