Design And Synthesis Of Tungsten Oxide-based Hydrogen-chromic Materials And Property Studies

Hydrogen（H₂）is a promising renewable energy carrier with the advantages of recyclability and cleanliness,but the leakage and supervision of hydrogen has always been a key issue in the application of hydrogen fuel.When the H₂ concentration is as low as 4%,it will explode when exposed to an open flame,and it is difficult to effectively monitor the leakage due to its colorless and odorless characteristics.In industrial production,hydrogen pipelines,valve interfaces,etc.are prone to H₂ leakage.The traditional hydrogen sensors are costly and complicated to install,and require conditions such as power-up and pressure during work,so their application environment is subject to certain restrictions.Compared with other detection methods,the visual hydrogen-chromic materials based on color changes have the advantages of safety and convenience.The coloring of transition metal oxides（TMOs）and metals（such as yttrium,palladium,etc.）have been used for H₂ gas detection.Among the color-changing transition metal oxides,tungsten trioxide（WO₃）is widely used in smart windows,gaschromic sensors and other fields due to its superior color-changing properties.Generally,WO₃ materials loaded with precious metals（Pt,Pd）can have a certain effect on hydrogen-chromic ability.Based on this,this article first starts from the perspective of WO₃ materials,prepares WO₃materials with different growth orientations by hydrothermal synthesis,and uses ethylene glycol reduction method to grow platinum nanoparticles in situ to synthesize Pt/WO₃ composite materials for hydrogen-chromic performance testing.Then,the performance optimization was carried out from the perspective of the precious metal Pt,and the pure platinum and Ag-Pt/WO₃bimetallic hydrogen-chromic materials were prepared by the sodium borohydride reduction method for performance research,and the structural changes during the discoloration process of the materials were preliminarily explored using in-situ characterization methods.The main findings are as follows:Using sodium tungstate as tungsten source,adding different additives,using hydrothermal synthesis to prepare three different growth orientation WO₃ materials,and synthesizing Pt/WO₃composite material by ethylene glycol reduction method.The results show that the difference of material growth orientation will affect the exposure of c-axis bridging oxygen,and then affect the diffusion distance of dissociated hydrogen.WO₃ nanowires have a relatively higher exposure ratio of c-axis bridging oxygen,which is conducive to dissociating H and the color change reaction of WO₃-based materials,promotes the hydrogen-chromic process,and improves the color change performance of the material.At the same time,the discoloration process will cause the material to evolve from low symmetry to high symmetry.Pt/WO₃ nanowires are selected for performance optimization,and performance comparisons are carried out by loading different amounts of platinum by the ethylene glycol reduction method,and the final loading is determined from the perspective of reducing the use of precious metals to reduce costs.Use sodium borohydride reduction method for performance optimization.Compared with ethylene glycol reduction method,the hydrogen-chromic performance of the material has been improved,and the recovery performance has been greatly improved.With the increase of air time,the material can basically return to the original state.Using in-situ characterization methods,the structural changes during the hydrogen-chromic of materials were preliminarily explored.The results showed that the discoloration of materials was directly related to the appearance of W⁵⁺,at the same time,the chemical environment and content of O ions have also changed.And the discoloration process will cause the material to evolve from low symmetry to high symmetry.The bimetallic materials were prepared by introducing Co,Ag,and Pd as secondary metals by sodium borohydride reduction method,and the synergistic effect of bimetals was used to promote or inhibit the hydrogen-chromic and recovery performance of Pt/WO₃ nanowire materials;As the second metal,Ag was further studied by changing its introduction sequence.The results showed that the introduction of Ag can improve the ability of the material to activate oxygen,which is beneficial to the recovery of the material from the colored state to the initial state.At the same time,it is found that the combination of Ag and Pt will affect the ability of Pt to activate hydrogen,and the discoloration performance of the material will be inhibited to a certain extent.