Palladium hexagonal nanoparticles/carbon nanotubes/cellulose nanocrystals integrated over paper for wearable hydrogen sensing with fast response by bridging behavior

Wearable hydrogen (H₂) sensing with fast response and excellent flexibility is highly desired for those workers who are exposed to flammable and explosive H₂, however, it needs further exploring. Here, wearable H₂ sensing with fast response at room temperature (∼25 °C) has been developed by integrating palladium hexagonal nanoparticles/carbon nanotubes/cellulose nanocrystals over filter paper (P-Pd HNPs/CNTs/CNCs). By optimizing the wet-chemical approach, Pd HNPs (edge length, ∼7.33 nm) have been synthesized via the simultaneous reduction of CNCs and ethanol, resulting in a random dispersion around the surface of cross-linked CNTs. Beneficially, P-Pd HNPs/CNTs/CNCs shows fast response/recovery time (3 s/3 s) to 0.5 v/v% H₂ and can detect 50 ppm H₂. Additionally, it exhibits excellent wearable sensing durability, including the resistance to freezing, pressing and peeling off the sensing materials. Theoretically, such fast-response H₂ sensing can be interpreted that H₂ is adsorbed over Pd to form PdHx intermediates, and the “bridging behavior” between CNCs and CNTs facilitates the H₂ diffusion and promotes electron hopping and tunneling. Potentially, this “bridging behavior” that contributes to fast-response H₂ sensing might be extended to other sensing materials for wearable gas detection.