A Research Of Pd-based Composite Thin Film Hydrogen Sensor

Hydrogen sensing technology is significant in many circumstances,such as in the synthesis process of ammonia and methanol,leak detection during shuttle launches,fuel cells ans so on.Palladium(Pd)has been widely used in hydrogen sensors for its noteworthy ability to absorb a large quantity of H2 and its high selectivity to H2.Pd based resistive H2 sensors have attracted much attention due to their simple device structure and fabrication process.First,in this thesis,the relationship between the response time of hydrogen sensor and the size of Pd nanoparticles is studied by using expansion dynamics theory.And then the porous nano Pd thin film based hydrogen sensor was prepared,and tested the performance of hydrogen sensor,including the dynamic response,response time,recovery time,sensitivity,and repeatability.It is found that porous nano Pd film based hydrogen sensors have a more rapid response and more stable performance compared with dense Pd membrane based hydrogen sensors.Then,the sensing performance of hydrogen sensors based on nanoporous Pd supported by AAOs was enhanced by pore-widening treatment of AAO using phosphoric acid(H3PO4)as etching solution.It is demonstrated that different concentrations of H3PO4 and different pore-widening time lead to different pore-diameters of AAO,resulting in different performance of hydrogen sensors.The optimized hydrogen sensor shows a fast response time of 19 s at hydrogen concentration of 1% and a detection range of H2 concentration from 0.1% to 2% by pore-widening treatment with a time of 30 min and 5% H3PO4 concentration.Further,in order to optimize the performance of the hydrogen sensor,the titanium dioxide(TiO2)layer was put into the porous nano Pd thin film based hydrogen sensor to form a porous nano Pd /TiO2 film hydrogen sensor.Then the effect of TiO2 layer thickness on the performance of hydrogen sensor was researched.When the TiO2 coating content is 1ml,the thickness of TiO2 layer is about the best performance of 10 nm hydrogen sensor.The response time is 5s and the recovery time reachs 9s while on the hydrogen concentration of 8000 ppm.At the same time,we have also analyzed the effect of TiO2 on layer the performance of hydrogen sensor and related mechanism.A novel carbon nanotubes and Pd nanocomposite thin films was introduced for hydrogen sensors.a new type of hydrogen sensor based on intersecting parallel singlewalled carbon nanotubes(SWCNT)and Pd nanocomposite thin films was introduced.The SWCNTs-Pd nanocomposite thin film was fabricated by depositing intersecting parallel SWCNTs on p-type silicon substrates using a two-step spray coating method and a Pd thin film by direct current magnetron sputtering.Hydrogen sensors based on intersecting parallel SWCNTs and Pd nanocomposite exhibit very fast response speed with a response time of 8s at 2% hydrogen gas.