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Hydrogen is an important biomarker for the human digestive system. However, accurate detection of ppm-level hydrogen in breath is difficult due to the competing detection of high concentration water. We fabricated Pt thin films that respond to hydrogen in air at concentrations as low as 500 ppb. In both dry and humid air, these films have almost identical response to hydrogen, i.e., their resistance decreases linearly with increasing hydrogen concentration regardless of relative humidity. Even at high relative humidity, these Pt thin films can detect ppm-level hydrogen. Furthermore, it was strongly suggested that these films can be applied to low-level hydrogen in the air expired by a healthy human. Based on the chemical kinetics, namely the adsorption and desorption of hydrogen and oxygen, the sensor response is quantitatively described by relating the hydrogen surface coverage to the magnitude of electron scattering at the Pt surface. The proposed model successfully reproduces the effects of hydrogen concentration and time on the sensor response, particularly at hydrogen concentrations below 20 ppm. Based on this model, these Pt thin film sensors have the potential to detect 1 ppm hydrogen in expired air within 30 s. [ABSTRACT FROM AUTHOR]

ZnO nanowires were grown on the active sensor surface of a surface acoustic wave (SAW) sensor via a vapour–liquid–solid (VLS) technique using pulsed laser deposition (PLD) as the particle source. The fabricated sensors were “delay-line” type (quartz substrate; ∼69.4-MHz central frequency). The nanowire length and diameter were controlled by the growth time and temperature, respectively. The sensor response at room temperature to various hydrogen (H 2 ) concentrations was recorded for different ZnO morphologies and nanowire thicknesses and compared with the performance of a thin-film sensor with a comparable amount of ZnO material. The sensor response depended on the ZnO volume and the morphology of the active surface. An increase in the ZnO volume enhanced the frequency shift for the same H 2 concentration, while the larger surface area of the longer nanowires enhanced the sensor response to low H 2 concentrations, enabling detection of concentrations as low as 0.01%. [ABSTRACT FROM AUTHOR]

Abstract: The development of reliable hydrogen sensors will facilitate the introduction of hydrogen to the natural gas infrastructure. One of the most promising configurations for such a device is a thin film based fiber optic sensor. We demonstrate that with such a device not only the measurement of a specific threshold partial pressure is possible, but also allows for a quantitative determination of the partial hydrogen pressure measured real-time and in-situ in the gas stream. The changing hydrogen pressure, up to 200mbar partial pressure, can be measured optically using a Pd–Au alloy thin film. However for the daily use of the sensor in the natural gas infrastructure it is important to determine the hydrogen sensing abilities under non-ideal conditions i.e. in gas mixtures containing high concentrations of CH4, C2H6, and C3H8. It is found that, the type of carrier gas (i.e. Ar (clean-conditions), CH4, C2H6, and C3H8) has hardly any influence on the measured hydrogen concentration and switching kinetics of the sensor. The sensor response times (hydrogenation kinetics) are comparable to those for clean H2 flows. [Copyright &y& Elsevier]