Metal–Organic Frameworks on Palladium Nanoparticle–Functionalized Carbon Nanotubes for Monitoring Hydrogen Storage

Palladium is a well-known hydrogen-absorbing material. When palladium is functionalized with copper(II) benzene-1,3,5-tricarboxylate (HKUST-1), a hydrogen-adsorbing metal–organic framework, its hydrogen-absorption capacity can be increased. In this work, we show that, by growing the HKUST-1 on palladium nanoparticle-functionalized single-walled carbon nanotubes (Pd NP/SWCNT), we can dynamically monitor the adsorption and desorption of hydrogen from the HKUST-1 and Pd NP composite by using the carbon nanotubes as transducers in chemiresistors. Addition of HKUST-1 to the Pd NP/SWCNT was shown to increase the sensitivity of the nanocomposite material to hydrogen by 300% and limit of detection to hydrogen by 33%. The increase in sensitivity was attributed to the increased hydrogen sorption capacity of the combined HKUST-1/Pd NP. A factor of 8 improvement in sensitivity was further achieved by using semiconductor-enriched SWCNT instead of mixed metallic/semiconducting nanotubes and a corresponding improvement in the theoretical limit of detection down to 70 ppb.