Hybrids composites based on metal oxide/carbon nanotubes or other carbon nanostructures are believed to provide many applications for gas sensing, exhibiting synergic effects between the metal oxides and carbon phases. Actually, we are carrying out researches in this field for developing new material compositions and/or synthesis procedures. In the present work, we focus on the preparation and characterization of MWNTs-Pt/TiO2 composites for hydrogen sensing in air. Hydrogen is one of the feasible candidates for replacing fossil fuels. Since hydrogen is flammable and explosive in concentrations higher than 4% in air, monitoring hydrogen leaks in the process of manufacturing, transporting, storage and in the filling station is essential. Nanostructured TiO2 has attracted considerable interest due to the superior properties such as large specific surface area and high uniformity, and has been largely investigated as hydrogen sensor [1, 2]. MWNTs can be embedded in the TiO2 matrix, so avoiding the agglomeration of TiO2 particles. Moreover, due to the high electrical conductivity carbon nanotubes provide a means to decrease the resistance of the sensing layer. Pt was used as an additive in order to enhance the sensitivity of the sensor, as reported in a previous paper [3]. The structure and morphology of the as-prepared MWNTs-Pt/TiO2composites were studied by SEM, TEM, XRD, and Raman spectroscopy. The typical nanostructure of composite materials is showed in the TEM image reported in Fig. 1. To fabricate the sensor device, MWCNTs-Pt/TiO2 samples were mixed with water, and the resulting paste was deposited as thick film on alumina substrates. Sensing tests were performed in an home-made apparatus that allows to operate at controlled temperature and to perform resistance measurements while varying the hydrogen concentration in the carrier stream. The sensor response is given by [(R-R0)/R0]×100, where R0 is the resistance baseline in synthetic air and R the resistance recorded under different hydrogen concentrations. Hydrogen sensing tests have shown that the MWCNTs-Pt/TiO2 device is sensitive to low hydrogen concentrations in air, unlikely the pure MWCNTs which display instead a negligible response. The sensor response at different H2 concentrations as a function of the operating temperature is reported in Fig. 2. Sensor operating at 150 °C exhibited the maximum response. In Fig. 3 is reported a typical dynamic response of the sensor operating at 150 °C to different pulses of hydrogen at a concentration between 0.5 and 3 %. The sensor shows a short response time, a critical parameter for the practical application as hydrogen leak sensor, whereas the recovery time is longer. Experiments with different metal oxides, carbon nanostructures and/or different preparation procedures are in progress in order to further understand the sensing properties of these composite materials and fabricate hydrogen sensors with enhanced performances.
Titania/MWCNTS Nanocomposites for Low Temperature Hydrogen Sensing
S Trocino;M Latino;
2012
Abstract
Hybrids composites based on metal oxide/carbon nanotubes or other carbon nanostructures are believed to provide many applications for gas sensing, exhibiting synergic effects between the metal oxides and carbon phases. Actually, we are carrying out researches in this field for developing new material compositions and/or synthesis procedures. In the present work, we focus on the preparation and characterization of MWNTs-Pt/TiO2 composites for hydrogen sensing in air. Hydrogen is one of the feasible candidates for replacing fossil fuels. Since hydrogen is flammable and explosive in concentrations higher than 4% in air, monitoring hydrogen leaks in the process of manufacturing, transporting, storage and in the filling station is essential. Nanostructured TiO2 has attracted considerable interest due to the superior properties such as large specific surface area and high uniformity, and has been largely investigated as hydrogen sensor [1, 2]. MWNTs can be embedded in the TiO2 matrix, so avoiding the agglomeration of TiO2 particles. Moreover, due to the high electrical conductivity carbon nanotubes provide a means to decrease the resistance of the sensing layer. Pt was used as an additive in order to enhance the sensitivity of the sensor, as reported in a previous paper [3]. The structure and morphology of the as-prepared MWNTs-Pt/TiO2composites were studied by SEM, TEM, XRD, and Raman spectroscopy. The typical nanostructure of composite materials is showed in the TEM image reported in Fig. 1. To fabricate the sensor device, MWCNTs-Pt/TiO2 samples were mixed with water, and the resulting paste was deposited as thick film on alumina substrates. Sensing tests were performed in an home-made apparatus that allows to operate at controlled temperature and to perform resistance measurements while varying the hydrogen concentration in the carrier stream. The sensor response is given by [(R-R0)/R0]×100, where R0 is the resistance baseline in synthetic air and R the resistance recorded under different hydrogen concentrations. Hydrogen sensing tests have shown that the MWCNTs-Pt/TiO2 device is sensitive to low hydrogen concentrations in air, unlikely the pure MWCNTs which display instead a negligible response. The sensor response at different H2 concentrations as a function of the operating temperature is reported in Fig. 2. Sensor operating at 150 °C exhibited the maximum response. In Fig. 3 is reported a typical dynamic response of the sensor operating at 150 °C to different pulses of hydrogen at a concentration between 0.5 and 3 %. The sensor shows a short response time, a critical parameter for the practical application as hydrogen leak sensor, whereas the recovery time is longer. Experiments with different metal oxides, carbon nanostructures and/or different preparation procedures are in progress in order to further understand the sensing properties of these composite materials and fabricate hydrogen sensors with enhanced performances.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
