Research On Optical Fiber Bragg Grating Hydrogen Sensors Based On Ion Intercalated Pt/MoO₃

With the consumption of fossil fuels,hydrogen has been recognized as a promising substitute to solve the future energy requirements.In addition,it has wide range of applications in the petrochemical,electronics and metallurgical industry.However,hydrogen is prone to leak during production,transportation,storage and utilizations due to its small molecule.Besides,it may explode in air at volume concentrations ranging from 4%to 75%.Therefore,it is urgent to develop hydrogen sensors with high sensitivity and fast response for safety.Compared to conventional hydrogen sensors based on electrical signals,which suffer from potential electrical sparks that may cause explosion in the presence of hydrogen,optical fiber hydrogen sensor is inherent safe and immune to electromagnetic interference by using optical parameters as sensing signals.At present,the FBG hydrogen sensor has the disadvantage of poor repeatability,which restricts the practical use of the sensor.In this paper,Pt/MoO₃ is used as hydrogen sensing material,the heat released by the reaction between the sening materials and hydrogen is conducted to the fiber bragg gratings?FBG?.The concentration of hydrogen in the environment is detected by monitering the change of the FBG's central wavelength The main contents of this paper are as follows:?1?The sensing material Pt/MoO₃ is prepared by hydrothermal method and experiments are made to obtain the sensor's parameters such as detection limit,measuring range,sensitivity and repeatability.It's found that the sensor based on Pt/MoO₃ exhibits a degradation phenomenon and the standard deviation is±18%.Pt/MoO₃ is characterized by XRD,SEM,TEM and Raman spectrum methods,the characterization results show that the severe degradation phenomenon can be ascribed to the phase transition of?-MoO3 during the reaction with hydrogen.?2?The method of enhancing the layer structure of?-MoO₃ by ion intercalation is put forward to inhibit the phase transition progress of?-MoO₃ and improve the repeatability of the sensor based on Pt/MoO₃.Na⁺intercalated Pt/MoO₃ are synthesized by hydrothermal method and the Na⁺amount in the sensing materials is controlled by adding different amount of NaCl in the precusors.The experiment results show that the Na⁺intercalation can improve the repeatability of Pt/MoO₃ effectively.The optimum NaCl amount in the precursor lies in 1mmol to achieve the best repeatability and the relative standard deviation of the sample in 50 tests is±1.9%,which increased an order of magnitude compared to Pt/MoO₃.XRD,SEM,TEM,ICP and Raman spectrum analysis reveal the mechanism of the increased repeatability.It's found that the intercalated ions will bond with the unshared oxygen atoms and the binding force between the layer of?-MoO₃ will transform from Van der Waals'force to ionic bonds.Thus,the stability of the layer structure is improved and the phase transition process is inhibited,which results in the improvement of the sensor's repeatability.?3?Li⁺and K⁺intercalated Pt/MoO₃ are prepared by hydrothermal method and the ion concentration is controlled by the amount of LiCl and KCl in the precursor.The results of the sensing performance test demonstrate that the repeatability of Pt/MoO₃ is dominated by kinds and concentration of intercalated ions.The optimum LiCl,NaCl and KCl amount in the precursors lies in 2 mmol,1 mmol and 1mmol to achieve the best repeatability.When the LiCl,NaCl and KCl amount in the precursors lies in 1mmol,it's found that the Na⁺intercalated Pt/MoO₃ exhibits the best repeatability among Li⁺,Na⁺and K⁺intercalated Pt/MoO₃.