Study On Preparation Of Transition Metal Compound/Carbon Nanofiber Composites And Their Electrocatalytic Performance Toward Hydrogen Evolution Reaction

In the 21 st century,energy and its related environmental problem have become the largest challenges towards the whole world.Hydrogen,a new kind of renewable and clean carrier for energy storage,has been widely concerned.The preparation of hydrogen by electrochemical methods from water supplies clean and high purity hydrogen.The key factor for electrolytic process is to select the appropriate catalyst with high catalytic activity.Currently,the most widely used catalysts are precious metals,such as Pt.But they can't be used widely for their high price and less storage capacity.Therefore,people pay more attention to produce orginal catalysts with low price and high performance through the composition adjustment,structure design and many other methods.The application of electrospinning technique has experienced more than one hundred years.At the beginning of the last century,scientists had explored it in the experiments and it gained the rapid development and improvement in recent decades.It is a good method for preparation of one dimensional nanofiberous materials.So far,hundreds of polymer nanofibers,inorganic nanofibers and even polymer/inorganic blend nanofibers have been made through this technique.Compared to the usual fibers,the electrospun micro/nanofibers can be used more widely in biomedical applications,sensors,catalysis and tissue engineering,solar cells,flexible device manufacturing and so on due to their outstanding properties such as higher porosity,higher specific surface area and stronger structural controllability.In this paper,the structure of the transition metal compound/carbon nanofiber composite materials is designed by using the electrospinning technique and in-situ polymerization approach.The carrier catalytic site density can be increased due to the nano catalytic active substance.The carbon nanomaterials and transition metal compounds can be recombined effectively.The introduction of one-dimensional carbon nanofibers in the composite materials improves the electrical conductivity and thus increases their catalytic hydrogen evolution and cycling stability.The high performance of non-noble metal electrochemical hydrogen evolution catalyst materials can be obtained through the following two parts.In this paper,the PMMA/?NH4?2Mo S4 composite nanofibers are obtained by electrospinning based on polymethyl methacrylate?PMMA?and ammonium thiosulfate??NH4?2Mo S4?.The surfaces of composite nanofibers are coated with polypyrrole?PPy?by means of in-situ polymerization.Then,the molybdenum disulfide?Mo S₂?/carbon nanofiber?CNF?composites with yolk-shell structure are obtained through high temperature carbonization.The composite fibers with yolk-shell structure can provide confined space for the formation of Mo S₂ fibers.The material shows optimum hydrogen evolution performance when the mass ratio of?NH4?2Mo S4 : PMMA is 1:2 due to the higher catalytic site density of Mo S₂ and the fast charge transfer between the core and shell.The onset potential??0?and the Tafels lope are 205 m V and 35.4 m V decade-1,respectively.The?NH4?2Mo S4/PMMA and?NH4?2WS4/PMMA composite nanofibers are prepared by electrospinning and are evenly coated with polypyrrole?PPy?,polyaniline?PANI?and polydopamine?PDA?by means of in-situ polymerization.The above three materials undergo carbonization and reduction at high temperature to obtain Mo S₂@NPPy-C,Mo S₂@-NPANI-C and Mo S₂@NPDA-C composite nanofibers.The Mo S₂@NPPy-C-0.01 shows optimum morphology and hydrogen evolution performance after regulating the concentration of the PPy.