Preparation Of Layer-expanded Two-dimension Transition Metal Chalcogenide Nanocomposite And Their Electrochemical Performance

With the depletion of fossil fuels and the deterioration of ecological environment,the new energy technology has become a hot research topic in the society.Electrical catalysis and energy storage as an important development direction of the development of new energy technologies,received extensive attention of contemporary scientific research workers.Two-dimonentional?2D?transition metal chalcogenides?TMC?compound and its composites as electrocatalysis of emerging and semiconductor materials have played a vital role in electrochemical catalytic hydrogen evolution reaction?HER?,oxygen evolution reaction?OER?and energy storage.Previous studies indicate that precise control for the structure,morphology,size and growth orientation of TMC helps to improve the performance of the electrical catalysis and energy storage.In this thesis,we adopt the different solvothermal methods to synthesize two-dimensional CoSe₂ and MoS₂ and their composites with different shape and size.Then,we obtain the stable structure,good performance of new catalytic materials and energy storage materials by optimizing the preparation conditions.Specific as follows:?1?An efficient HER electrochemical catalyst has been developed through an in-situ reduction of ammonium tetrathiomolybdate?ATTM?on carbon fibers?CFs?to afford layer-expanded MoS₂/CFs composites?LE-MoS₂/CFs?.X-ray diffraction?XRD?indicates the interlayer of MoS₂ nanosheets was expanded with d spacing 0.99 nm,and transmission electron microscopy?TEM?shows the lattice distance as 0.99 nm,which is agreed with XRD data.Because of MoS₂ can provide more the active site and conductive material CFs can improve electron transfer rate,we can get the optimal preparation conditions of electric catalyst by regulating the mole ratio of Mo/C.The HER test shows that the LE-MoS₂/CFs with Mo/C molar ratio of 0.04 has the highest catalytic activity with the lowest overpotential?131 mV vs.RHE?and the highest current density(10 mA cm^-2 at 200 mV vs.RHE).?2?An efficient hydrogen evolution cathode was developed by in-situ growth of lamellar structured cobalt diselenide?CoSe₂?nanosheets on the surface of commercial titanium?Ti?plate?CoSe₂NS@Ti?in the first time.Both SEM images and XRD data confirmed that the Ti plate is homogeneously coated by few stacking layers of lamellar structured CoSe₂,which could provide more active sites for hydrogen evolution reaction?HER?.This catalytic cathode shows exceptionally high activity for hydrogen evolution with 152 mV overpotential to afford a current density of 10 mA cm^-2 and a high exchange current density of 5.01×10^-3 mA cm^-2,as well as high cyclic stability with negligible decrease of cathodic current after 500 cycles.?3?An efficient self-supported electrode was developed by in-situ growth of interlayer expanded lamellar cobalt diselenide?CoSe₂?nanosheets?NS?on carbon paper?CP?substrate?CoSe₂ NS@CP?.This rationally designed nanostructure can provide more active sites for both hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.The bifunctional electrode exhibits high electrocatalytic performance with-128 mV onset potential for the HER in 0.5 mol L^-1 H₂SO₄ and+1521 mV for the OER in 1.0 mol L^-1 KOH.Besides,small overpotentials of 201.1 mV and 1636 mV are needed to drive the HER and OER at current density of 100 mA cm^-2.The catalyst was tesed in two electrode system.The results showed both excellent catalytic activity with overall current density of 100 mA cm^-2 at2.13 V and tremendous durability with negligible decrease in potential at a constant current of20 mA cm^-2 for more than 30 hours.It shows that the CoSe₂NS@CP electrode has very profound application in water splitting.?4?A novel way to prepare incompact MoS₂ nanosheets assembled nanorods has been demonstrated with the interlayer of MoS₂ nanosheets expanded to 0.89 nm,namely LE-MoS₂NRs.The material was characterized by XRD,XPS and electron microscopes.The XRD data and HRTEM images confirmed the existence of expanded interlayer of MoS₂ nanosheets.N₂adsorption-desorption isotherms of LE-MoS₂ NRs indicated high specific area up to 37.0 m²g^-1.It was found that the expanded interlayer spacing can benefit the ion transportation within the MoS₂ interlayers.The as-prepared electrode material showed capacitance up to 231 F g^-1at 1 A g^-1 charge-discharge current and cycling stability test indicated high capacitance of 177F g^-1 was retained after 1000 cycles.