Microcapillary Evanescent Wave Hydrogen Sensor Based On Nano-palladium Film

As one of the main representatives of new energy,hydrogen has attracted more and more attention in various fields.However,because hydrogen has an explosion risk when the concentration of hydrogen is higher than 4%,the sensitive detection of low concentration hydrogen in hydrogen application environment is very important.In recent years,in order to develop a new generation of hydrogen sensors with rapid response,high sensitivity,small size and low cost,researchers have made continuous exploration.In this paper,an optical fiber-capillary evanescent wave sensor based on microcapillary is proposed.By depositing a palladium film on the surface of the microcapillary,a fast and sensitive response of the sensing structure to hydrogen is achieved.The micro-capillary-based optical fiber evanescent wave sensing structure utilizes the total reflection effect of light in the tube wall to realize the evanescent field excitation.By monitoring the evanescent field interacting with the palladium film on the surface of the tube wall,the light signal changes are monitored to reflect the hydrogen concentration in the external environment changes.We used the sensors to detect hydrogen at concentrations of 1%,2%,and 4%.The experimental results show that the sensor has a sensitive response to the change of external hydrogen.In addition,we carried out nano-patterning on the palladium film of the microcapillary-based evanescent wave sensor.Using a self-assembled polystyrene microsphere as a template,a layer of palladium nanoparticles was prepared on the surface of the microcapillary sensing area.Compared with palladium membranes,nano-palladium particles have a large relative volume ratio,high specific surface area,many surface active sites,and the crystal facet effects with high surface reactivity,which can increase the rate of absorption and desorption of the reaction.We compared and analyzed the spectral responses of different hydrogen concentrations using sensor elements with nano-palladium membranes.Experimental results show that for the same hydrogen concentration,the wavelength response of the evanescent wave sensor based on palladium nanoparticles is significantly smaller than that of a sensor with a complete palladium film,which means that the stress response caused by the expansion of a part of the palladium film is excluded from the response.Therefore,when the palladium film particle evanescent wave sensor is used to evaluate the complex dielectric constant of the palladium film,the measurement accuracy can be effectively improved.Since then,we have improved the above microcapillary-based fiber evanescent wave sensing structure,and obtained a new Mach-Zehnder interferometer,which was used for hydrogen sensing and air refractive index measurement.The experimental results show that the Mach-Zehnder interferometer can provide a refractive index resolution of up to 7.57×~uRIU,considering the sensitivity of the sensor and the performance level of the detector used.In this paper,a capillary-based optical fiber evanescent wave sensor is designed and prepared,and it was successfully used for hydrogen concentration detection,palladium material complex dielectric constant measurement and gas refractive index detection.The sensor has the advantages of high sensitivity,fast response and low cost,and has good application potential in the field of gas sensing.