Hydrothermal growth of overlapping ZnO nanorod arrays on the porous substrate and their H2 gas sensing

ZnO nanorod arrays (ZNAs) were prepared on a metakaolin (MK)-based porous substrate via a seeding-hydrothermal method. The spherical poly methyl methacrylate (PMMA) microspheres were employed as the pore former to obtain homogeneous porous structure on the MK-based substrates. Various characterization methods were used to investigate the effects of the porous structure on the morphological and structural properties of the ZNAs. The results indicated that the alignment degree of the ZNAs decreased significantly with the enhancement of the apparent porosity of the substrate. The ZNAs prepared on the MK-based substrate with the PMMA content of 30 wt% exhibited an overlapping morphology with an average diameter and length of 88 nm and 570 nm, respectively. Gas sensing measurements revealed that the response value of the overlapping ZNAs to 1000 ppm H2 at the operating temperature of 225 °C was 9.2, which is four times higher than that of the vertical ZNAs grown on the MK-based non-porous substrate. It confirms that the porous structure of the as-prepared substrates favors for the growth of the overlapping ZNAs, and the enhanced H2 gas sensing performance might be primarily related to the more effective adsorption sites and the modulation of the potential barrier at the junctions of the overlapping morphology. •Gas sensor based on the ZNAs was prepared on a metakaolin-based porous substrate.•The porous structure of the substrate facilitated the growth of overlapping ZNAs.•Enhanced sensing properties were mainly ascribed to the potential barrier effect between the cross-linked contact of the overlapping ZNAs.