Hydrogen sensing performance of electrodeposited conoidal palladium nanowire and nanotube arrays

Conoidal palladium nanowire and nanotube arrays were fabricated by electrochemical deposition into the branched pores of an alumina template. The formation of nanostructures was controlled by analysing current–time transients during electrodeposition. The sensor response to hydrogen gas was investigated in the arrays of just formed nanotubes and nanowires. The dominant sensing signal was increment of conductivity due to the contact improvement by volume expansion of nanowires and nanotubes. Without proper activation treatment, however, the sensing signal was not stable. A few cycles of hydrogen loading–unloading on the conoidal nanotubes dramatically enhanced the stability in hydrogen sensing performance. It was based on the formation of break junctions after exposure of conoidal palladium nanotubes to 1–2.5% H2, which also leaded to fast response on hydrogen concentration as small as 0.1% and small relaxation time when hydrogen was released.