Room temperature hydrogen sensor for the detection of flammable concentrations based on SWCNT modified by a solid solution of oxygen in Pd nanoparticles

Abstract

Fabricating a high-response sensor for the repeatable detection of a high (flammable) hydrogen concentration (4 %) at room temperature with long-term stability remains a challenge. Here, a hydrogen (H2) sensor based on single-walled carbon nanotubes (SWCNTs) functionalized with palladium (Pd) nanoparticles of a previously unexplored structure is demonstrated. The active sensing layer is fabricated via airbrush deposition of SWCNTs and pulsed laser ablation of Pd in a vacuum. Complementary characterization techniques, including HRTEM, electron diffraction, STEM-EELS, Raman spectroscopy, and XP-spectroscopy, reveal that the Pd nanoparticles form a solid solution of oxygen in metallic Pd (Pd+O), partially covered with a two-dimensional palladium oxide (PdO) layer. The Pd+O/PdO nanoparticles exhibit an expanded face-centered cubic (FCC) and cubic primitive lattice, representing a previously unreported Pd structure. The sensor achieves a repeatable 203 % response to 4 % H2 at room temperature and operates over a wide concentration range (0.05 % – 10 % H2 in air) with long-term stability exceeding 1.5 years. The detection mechanism is hypothesized to involve ionosorption and/or oxygen vacancies in the PdO layer. These findings highlight the undiscovered potential of carbon nanostructure/Pd nanoparticle hybrids for enhanced hydrogen sensing through Pd structure tailoring.