Palladium -based hydrogen sensors

There are three major classes of palladium-based hydrogen sensors [4], The most popular class of palladium-based sensors is based on palladium resistors. A thin film of palladium deposited between two metal contacts shows a change in conductivity on exposure to hydrogen due to the phase transition in palladium. The palladium field-effect transistors (FETs) or capacitors constitute the second class, wherein the sensor architecture is in a transistor mode or capacitor configuration. The third class of palladium sensors includes optical sensors consisting of a layer of palladium coated on an optically active material that transforms the hydrogen concentration to an optical signal. 

Operation Mechanisms of Solid-State Sensors 15.3.1 Theory of Palladium-Based Hydrogen Sensors... 

Several types of palladium-based hydrogen sensors have been reported in the literature. The most notable ones are based on Pd thin-film resistors, FETs, Pd nanowires, Pd nanoparticle networks, Pd nanoclusters, and Pd nanotubes as shown in Table 15.2. 

Another p-n junction-based hydrogen sensor has been produced by implanting palladium ions into 6H n-type SiC material [67]. Gold-plated copper contacted the p-n junction device. The gas response was measured as (small) changes in current as the gas ambient was varied between air and 4% in argon in the temperature range 23-240°C. For an absolute voltage above 1.2V, the p-n junction broke down. 

Silva SF, Coelho L, Frazao O, Santos JL, Malcata FX (2012) A review of palladium-based fiber-optic sensors for molecular hydrogen detection. IEEE Sensors J 12(1) 93-102 Skucha K, Fan Z, Jeon K, Javey A, Boser B (2010) Palladium/silicon nanowire Schottky barrier-based hydrogen sensors. Sens Actuators B 145 232-238... 

Zalvidea, D., Diez, A., Cruz, J.L. and Andres, M.V., A wavelength multiplexed hydrogen sensor based on a palladium-coated fibre taper and a Bragg grating, Electron, 40, 301, 2004. 

Fig. 13.10a. An MNF was coated with an ultra thin palladium film. The operational principle of this sensor was based on the fact that a thin palladium film has the ability to selectively absorb hydrogen. If a palladium film is exposed to hydrogen, its refractive index, and, in particular, absorbance, changes. The change in refractive index causes a change in transmission power of an MNF. The MNF fabricated in Ref. 15 had a palladium film of 4 nm in thickness and 2 mm in length. In Fig. 13.10b, the transmission power of the MNF is shown as a function of time when the sensor was exposed successively to a 3.9% concentration of hydrogen. The response time calculated from the plot was 10 s. This response time is 3 5 times faster than that of other optical hydrogen sensors and about 15 times faster than that of some electrical nano hydrogen sensors. The fast response of the sensor is, presumably, due to the ultra small thickness of the palladium film that is rapidly filled with hydrogen. Figure 13.10c shows the transmission of this sensor as a function of time for...

Fig. 9.19 Palladium micro mirror sensor for hydrogen based on changes of reflectivity (adapted from Butler, 1991)...

Dong B, Zhong DY, Chi LF, Fuchs H (2005b) Patterning of conducting polymers based on a random copolymer strategy toward the facQe fabrication of nanosensors exclusively based on polymers. Adv Mater 17 2736-2741 Favier F, Walter EC, Zach MP, Benter T, Penner RM (2001) Hydrogen sensors and switches from electrodeposited palladium mesowire arrays. Science 293 2227-2231... 

Lith JV, Lassesson A, Brown SA, Schulze M, Partridge JG, Ayesh A (2007) A hydrogen sensor based on tunneling between palladium clusters. Appl Phys Lett 91 181910... 

As has been demonstrated, the fields of quartz crystal microbalance (QCM)- and surface acoustic wave (SAW)-based gas sensors are also of interest in metal film application (Miura 1991 Jakubik etal. 2003 Jakubik and Urbanczyk 2005). When the palladium or palladium-based alloy layer absorbs hydrogen, both its mass density and electrical conductivity change, and this produces a detectable change in the frequency of the SAW and resonance frequency of (JCM. Devices were able to detect hydrogen gas in a range of 1.5-4.0% concentration in air. 

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