(Invited) Development of Fiber-Optic Hydrogen Sensor Using Platinum-Supported Tungsten Trioxide-Silica Composite Film
Authors: Okazaki Shinji , Ishii Erika , Nishijima Yoshiaki , Arakawa Taro 
Published: December 2024

Hydrogen has been attracting attention in recent years as a clean energy carrier that can be easily obtained by converting water into hydrogen by using various renewable natural energy resources and enable to generate energy through chemical reaction without emitting pollutants. While it has these advantages, hydrogen gas is characterized by two dangerous properties: low ignition energy and wide combustion range. Furthermore, leakage of hydrogen is difficult to detect because of its properties such as colorless, transparent, and odorless. Therefore, a leakage detection system is indispensable for the safe handling of large amounts of hydrogen energy carrier. So far, various high-performance sensors have been proposed and practically utilized. However, developments of sensor devices which can be operated at room temperature are still challenge. Furthermore, there are significant needs for distributed measurements for leakage detection of large-scale hydrogen infrastructure. In this study, fiber-optic techniques that can easily and inexpensively capture hydrogen leakage in a wide spatial area are focused to realize a line-type hydrogen sensor. In order to develop such kind of fiber optic hydrogen sensor, platinum-supported tungsten oxide film and tungsten-silica composite film were utilized as hydrogen-sensitive materials whose optical properties are significantly change through the reaction with hydrogen. A plastic-clad quartz core fiber with a core diameter of 200 μm and a cladding diameter of 230 μm (H-PCF: manufactured by Sumitomo Electric Industries) was used. In order to immobilize the hydrogen-sensitive cladding, the cladding was removed using an organic solvent. Then, the hydrogen-sensitive materials were directly coated on fiber core and immobilized by calcination in air at different temperatures. The sensing mechanism is based on the evanescent field interaction in the hydrogen sensitive clad region. As a first step, transmission spectra of sensing film itself under air and hydrogen atmosphere were evaluated for optimizing wavelength of the light source used in the sensor system. The transmittance of the sensitive film decreased in the range of wavelengths above about 500 nm after exposure to pure hydrogen, and the decrease at 1300 nm was greater than that at 850 nm, suggesting that the 1300 nm wavelength is more likely to extract changes in optical properties caused by the response (Fig. 1). Then, fiber optic sensor device was fabricated, and the amount of propagating light was measured using LED light sources at wavelengths of 850 nm and 1300 nm. In the case of using the light source with a wavelength of 1300 nm, the light attenuation rate with respect to the hydrogen response was nearly twice and the response speed was faster, compared with those at 850 nm. Therefore, it was concluded that a light source with a wavelength of 1300 nm for measurement of propagating light intensity is suitable for monitoring hydrogen leakage.

Figure 1