Palladium nanowire hydrogen sensor

Palladium nanowires, synthesized by template-nanomanufacturing techniques, has been studied for hydrogen gas sensing applications at room temperature. In this study parallel arrays of Pd nanowires were fabricated by electrodeposition from an aqueous plating solution onto an HOPG surface. The nanowires were then transferred onto a polystyrene film and silver electrical contact pads were fabricated by shadow masking. The morphology of the nanowires was analyzed using atomic force microscope (AFM) in noncontact mode and the diameter of the observed nanowires was measured to be approximately 250nm. Scanning electron microscope (SEM) images revealed that the nanowires fabricated by this procedure were parallel and continuous. Experimental results indicated that the sensors are highly sensitive to hydrogen, showing a two-order change in conductance. The morphology of the nanowires was analyzed using SEM and AFM in order to understand the properties responsible for the high sensitivity of the nanowires. SEM images showed that the nanowires contain nanogaps in absence of H₂. On, exposure to H₂ palladium absorbed hydrogen resulting in the expansion of Pd grains. This expansion results in the closing of the nanogaps. The expansion occurred due to the phase transition from alpha to beta and the palladium lattice expansion.