The Synthesis Of MoSe₂/Carbon Nanofibers Hybrids And Their Hydrogen Evolution Reaction Performance

Energy and environmental issues are two crucial themes for the sustainable development of human society.With the rapidly growth of population,social development and environmental pollution,human beings must continue to seek for novel,efficient and environmental friendly renewable energy.Hydrogen,a promising efficient,clean and sustainable energy carrier,is believed to be the ultimate energy for human beings.The development and utilization of hydrogen energy is of great significance to solve the energy crisis and environmental pollution.Water splitting is one of the most effective and facile method to produce hydrogen.Traditionally,members of the Pt group have been regarded as the best electrochemical catalyst for the hydrogen evolution reaction?HER?,however,their high cost and scarcity limit their extensive applications.Therefore,non-previous and abundant HER catalysts are highly desired.Due to the high abundant and electrochemical acitivity,transition metal dichalcogenides?TMDs?have become the hotspot of research on cathodic catalysts for hydrogen evolution reaction.Many researches suggested that the activites of TMDs' catalysts depend on their exposed active edge sites.Hence,it is crucial to maximumly expose the active edge sites and promoted the effience of catalysts.Due to the characteristics of three-dimensional network structure,high electron transport capability and excellent chemical stability,carbon nanofibers?CNFs?can improve the electron transport ability of TMDs and thus enhance the HER activities of TMDs.In the present investigations,we prepared the PAN or PVA nanofiber membrane by electrospinning technology,and then we obtained the CNFs by carbonization of them.Subsequently,we synthesized the MoSe₂ and MoS_2?1-x?Se_2x by CVD method and we obtained a series of molybdenum diselenide/carbon nanofibers hybrid materials with different morphologies,size and structures.Then the relationship between the microstructure of the hybrid materials and the catalytic activity for hydrogen evolution were studied.?1?We prepared MoSe₂/CNFs hybrids based on the substrate of CNFs by CVD method.Triangular MoSe₂ nanoflakes vertically growed on the surface,and they exihibited a high crystallinity.In the acid solution,the results of HER reveal that the the hybrids exihibited significantly enhanced catalytic activity and excellent stability.The onset potential of MoSe₂/CNFs hybrids is 69 mV,and the slope of Tafel is approximately 107 mV dec-1 and high current density.The research suggests that the structure of vertical alignment on the surface of CNFs could maxiumlly expose the active edge sites of MoSe₂ nanoflakes,resulting in significantly enhanced catalytic activity.?2?We obtained MoS_2?1-x?Se_2x/CNFs hybrids with different morphologies and structures by doping of MoSe₂ with S element and adjusting the ratio of S/Se.The results of characterization and analyzation indicate that MoS_2?1-x?Se_2x/CNFs hybrids exihibited high crystallinity and in the case of ternary alloy MoS_2?1-x?Se_2x,the mixing of Se and S is on the atomic scale and without the phase separation of MoS₂ and MoSe₂.We evaluated the HER performance of ternary alloy,and it demonstrates that the onset potential of MoS_2?1-x?Se_2x?HD?/CNFs hybrids?x=0.78?is 54 mV and the slope of Tafel is fitted to be 144 mV dec-1.In the case of MoS_2?1-x?Se_2x?LD?/CNFs hybrids?x=0.64?,the onset potential and the slope of Tafel is 104 mV and 124 mV dec-1,respectively.The structures of ternary alloy MoS_2?1-x?Se_2x nanoflakes were changed by the doping of S element,resulting that the alloy could maximally expose active edge sites and optimize HER performance.Hence,MoS_2?1-x?Se_2x/CNFs hybrids exihibited much higher HER performance.?3?MoO₃ can be obtained by the thermal decomposition of ?NH₄?₂MoO₄,therefore we take advantage of the property and then dissolved the?NH₄?₂MoO₄ into the PVA aqueous solution.And then we obtained the PVA-Mo nanofiber membrane by electrospinning.Subsequentlly,we in situ prepared the MoSe₂ @CNFs and MoS_2?1-x?Se_2x@CNFs hybrids.The results of characterization and evaluation demonstrate that there are of siginificantly difference in the morphologies,structures and activities of HER between the hybrids grown by in situ method and CVD method.It is difficult to expose the active edge sites of hybirds grown by in situ method,hence,the HER performance is much lower for hybrids.