Hydrogen sensing properties of multi-walled carbon nanotubes

The hydrogen sensing properties of multi-walled carbon nanotubes (MWNTs) synthesized by a hot filament CVD process are reported in this paper. The MWNTs were synthesized by a hot filament assisted chemical vapor deposition method using cobalt oxide nanoparticles as the catalyst on SiO2 surfaces. The MWNTs were characterized with Raman spectroscopy and scanning electron microscopy. Two-terminal test devices were fabricated by depositing a layer of MWNTs between prefabricated gold electrodes on SiO2 surfaces. The diameter of these MWNTs was in the 5-8 nm range. The sensitivity of carbon nanotubes was measured for different gas concentrations at different temperatures. It was found that the MWNTs were sensitive to H-2 ill low temperature regions of 140-350 degrees C and had a maximum sensitivity (80%) at 230 degrees C. No sensitivity was observed at a temperature lower than 140 degrees C or higher than 400 degrees C. Though bare MWNTs are not sensitive to H-2 at room temperature, they exhibited very good sensing characteristics in the 140-300 degrees C range. (C) 2008 Elsevier B.V. All rights reserved.