Crystalline Nanodiamond-Induced Formation of Carbon Nanotubes for Stable Hydrogen Sensing

Herein, multiwalled carbon nanotubes (MWCNTs) were synthesized through a two-step chemical vapor deposition process via an ultra-nanocrystalline diamond (ND) as a carbon source for the first time, and no gaseous carbon molecules were used during CNT growth. A unique core–shell-like morphology was revealed from the high-resolution transmission electron microscopy (HRTEM) microstructure in which the CNT is covered by nanodiamond grain boundaries. The NDCNT is then fabricated with a metal interdigitated electrode to form hydrogen sensors. The as-fabricated NCDNT exhibits a higher gas sensor response toward H₂ gas than the as-fabricated ND films. Moreover, the present NDCNT sensor shows rapid response/recovery during the H₂ adsorption/desorption process and shows high selectivity. It also exhibits long-term stability and repeatability over 2 months without perceptible degradation. This can be attributed to the present NDCNT structure that has defect sites from nanodiamond grains and contributes numerous binding sites for the H₂ gas molecules. The present sensor shows rapid recovery compared with previously reported studies due to the H₂ spillover mechanism. This strategy allows the facile synthesis of ND-induced CNT growth and achieves high H₂ sensing performance via a scalable method.