Abstract:We report for the first time on the experimental response of a Surface Plasmon Resonance fiber optic sensor based on wavelength modulation for hydrogen sensing. This approach of measuring the hydrogen concentration makes the sensor insensitive to intensity fluctuations. The intrinsic fiber sensor developed provides remote sensing and enables the possibility of multi-points sensing. The sensor consists of a multilayer of 35 nm Au / 180 nm SiO 2 / Pd deposited on a step-index multimode fiber core. The sensitivity and selectivity of the sensor are optimal at a Pd thickness of 3.75 nm. The sensor is sensitive to a hydrogen concentration ranging between 0.5 and 4% H 2 in Ar, with a response time less than 15 s.

There is a great interest in the development of reliable and low-cost hydrogen sensors for applications in the hydrogen economy, industrial processes, space application, detection of environmental pollution, and biomedical applications. Here, a new type of optical detector that indicates the presence of hydrogen in concentration range 5 ppm to 0.1 vol% H 2 merely by a reversible and tunable color change is reported. The device takes advantage of the reversible change in optical properties of a Pd-capped Y thin fi lm upon exposure to H 2 , while the color is tuned using the interference of light refl ected between the Y and Pd layers. In this way, an eye-readable optical sensor that circumvents the need for electronics and external digital readouts is created. Using surface modifi cations, the performance of the H 2 detector in humid and oxygen rich environment is greatly improved. Therefore, the device has the potential to be used for chemical and also biochemical/biomedical H 2 sensing applications such as breathe hydrogen tests.

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The catalytic properties of Pd alloy thin films are enhanced by a thin sputtered PTFE coating, resulting in profound improvements in hydrogen adsorption and desorption in Pd-based and Pd-catalyzed hydrogen sensors and hydrogen storage materials. The remarkably enhanced catalytic performance is attributed to chemical modifications of the catalyst surface by the sputtered PTFE leading to a possible change in the binding strength of the intermediate species involved in the hydrogen sorption process.

The structural, thermodynamic and optical properties of Mg 2 Ni thin films covered with Pd are investigated upon exposure to hydrogen. Similar to bulk, thin films of metallic Mg 2 Ni take up 4 hydrogen per formula unit and semiconducting transparent Mg 2 NiH 4−␦ is formed. The dielectric function ⑀ of Mg 2 Ni and fully loaded Mg 2 NiH 4−␦ is determined from reflection and transmission measurements using a Drude-Lorentz parametrization. Besides the two "normal" optical states of a switchable mirror-metallic reflecting and semiconducting transparent-Mg 2 NiH x exhibit a third "black" state at intermediate hydrogen concentrations with low reflection and essentially zero transmission. This state originates from a subtle interplay of the optical properties of the constituent materials and a self-organized double layering of the film during loading. Mg 2 NiH 4−␦ preferentially nucleates at the film/substrate interface and not-as intuitively expected-close to the catalytic Pd capping layer. Using ⑀ Mg 2 Ni and ⑀ Mg 2 NiH 4 and this loading sequence, the optical response at all hydrogen concentrations can be described quantitatively. The uncommon hydrogen loading sequence is confirmed by x-ray diffraction and hydrogen profiling using the resonant nuclear reaction 1 H͑ 15 N,␣␥͒ 12 C. Pressure-composition isotherms suggest that the formation of Mg 2 NiH 4−␦ at the film/substrate interface is mainly due to locally enhanced kinetics.