Uniformly dispersed Pt-Ni nanoparticles on nitrogen-doped carbon nanotubes for hydrogen sensing

Nitrogen-doped multiwall carbon nanotubes (NCNTs), having an average diameter of approximately 20 nm, were synthesized at 650 °C by chemical vapor deposition using a pyridine precursor. Pt-Ni alloyed nanoparticles with approximate diameter 3 nm and with different Pt to Ni molar ratios were deposited on the NCNTs by a microwave-polyol method. Electron microscopy revealed that the nanoparticles were deposited homogeneously on the outer surface of the NCNTs and were immobilized at active nitrogen sites. A dielectrophoresis technique was used to selectively align the Pt-Ni-coated NCNTs between metallic electrodes to form conductometric hydrogen gas sensors. Gas sensing measurements performed with different concentrations of hydrogen revealed that the sensor based upon Pt/NCNTs exhibited the fastest response and recovery and best sensitivity. The sensing mechanism in the Pt/NCNT sensors can be explained by a combination of responses from the nitrogen-induced defects and the supported Pt nanoparticles, with the latter providing significantly faster response and recovery.