Sub-6 nm Palladium Nanoparticles for Faster, More Sensitive H2 Detection Using Carbon Nanotube Ropes.

Palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP) are used as the sensing element for hydrogen gas (H2) chemiresistors. In spite of the fact that Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces, CNT@PdNP ropes produce a relative resistance change 20-30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H2 sensing metrics (speed, dynamic range, and limit-of-detection), relative to single Pd nanowires which heretofore have defined the state-of-the-art in H2 sensing performance. Specifically, response and recovery times in air at [H2] ≈ 50 ppm are one-sixth of those produced by single Pd nanowires with cross-sectional dimensions of 40 × 100 nm Pd. The LODH2 is <10 ppm versus 300 ppm, and the dynamic range (10 ppm -4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (±1) nm to 5.8 (±3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems.