Self-Assembled Hierarchical Interfaces of ZnO Nanotubes/Graphene Heterostructures for Efficient Room Temperature Hydrogen Sensors

Herein, we report the novel nanostructural interfaces of self-assembled hierarchical ZnO nanotubes/graphene (ZNT/G) with three different growing times of ZNTs on graphene substrates (namely, SH 1, SH 2, and SH 3 ). Each sample was fabricated with interdigitated electrodes to form hydrogen sensors, and their hydrogen sensing properties were comprehensively studied. The systematic investigation revealed that SH 1 sensor exhibits an ultrahigh sensor response even at a low detection level of 10 ppm (14.3%) to 100 ppm (28.1%) compared to those of the SH 2 and SH 3 sensors. The SH 1 sensor was also found to be well-retained with repeatability, reliability, and long-term stability of 90 days under hydrogenation/dehydrogenation processes. This outstanding enhancement in sensing properties of SH 1 is attributed to the formation of a strong metalized region in the ZNT/G interface due to the inner/outer surfaces of ZNTs, establishing a multiple depletion layer. Furthermore, the respective band models of each nanostructure were also purposed to describe their heterostructure, which illustrates the hydrogen sensing properties. Moreover, the long-term stability can be ascribed by the heterostructured combination of ZNTs and graphene via a spillover effect. The salient features of this self-assembled nanostructure are its reliability, simple synthesis method, and long-term stability, which makes it a promising candidate for new generation hydrogen sensors and hydrogen storage materials.