Modification Of Nitrogen-doped Carbon Tubes With Transition Metal Sulfoselenide And Their Photo-and Electro-chemical Properties

Carbon nanotubes have excellent mechanical,electrical and electrochemical properties,and have good application prospects in the fields of catalysts,field emission and hydrogen storage materials.In this paper,a series of nitrogen-doped carbon nanotubes and their nanocomposites were synthesized by using graphitic carbon nitride（g-C₃N₄）as precursor.The purpose of this study is to improve the optical/electrochemical properties of nitrogen-doped carbon nanotubes through morphology control,element doping and heterostructure construction,and then to explore their applications in photocatalysis,electrocatalysis,energy storage and conversion.The specific research contents are as follows:The influence of Co on the formation process of nitrogen-doped carbon nanotubes and the evolution of photo/electrochemical properties.Nitrogen-doped carbon nanotubes were prepared by secondary thermal polymerization with g-C₃N₄ as precursor.The influence of Co on the formation process of nitrogen-doped carbon nanotubes at different temperatures（660-780°C）and the evolution of photo/electrochemical properties were investigated.The formation of tubular morphology can be observed after 680°C in the presence of Co.With the increase of secondary thermal polymerization temperature and cobalt doping,the photocatalytic activity of Co-CN gradually decreases,while the electrochemical performance gradually improves.Compared with commercial carbon nanotubes,nitrogen-doped carbon nanotubes（Co-CNTs）embedded with cobalt nanoparticles have better conductivity and larger specific surface area.On the one hand,the sample has better electrocatalytic hydrogen evolution ability in acidic medium,and the best sample overpotential is only 249 m V(10 m A cm^-2).On the other hand,it also shows a certain application potential of supercapacitors,and the specific capacitance can reach 400 F g^-1(1 A g^-1).The composite conductive base material with good electrochemical performance is obtained,which lays the foundation for the next step of synthesizing high-performance electrocatalysts.Modification of nitrogen-doped carbon nanotubes with Mo Se₂ nanoparticles and its electrocatalytic properties.In order to expand the application range of nitrogen-doped carbon nanotubes,we can further put them into practical application,so as to obtain more efficient electrocatalysts with HER and OER activities.Co-CNTs-Mo Se₂ heterostructure was synthesized by one-step solvothermal reaction.The large specific surface area of Co-CNTs is beneficial to the uniform distribution of Mo Se₂,thus exposing more active sites.Due to the synergistic effect of Mo Se₂ and carbon nanotubes,the catalyst showed excellent electrocatalytic activity.When the current density is 10 m A cm^-2,the overpotential of Co-CNTs-Mo Se₂electrode in alkaline medium are 272 m V（HER）and 353 m V（OER）,respectively.The whole electrolyzed water device can keep the current density of 10 m A cm^-2 for a long time when the driving voltage is as low as 1.7 V,and the potential attenuation is almost negligible.This experimental result provides an idea for the synthesis of bifunctional electrocatalysts with low cost and high performance in alkaline medium.Modification of nitrogen-doped carbon nanotubes with Ni S₂ nanoparticles and its electrochemical properties.In order to obtain multifunctional electrocatalysts in alkaline medium,Ni S₂ was loaded on carbon nanotubes embedded with cobalt nanoparticles.The catalyst not only has excellent electrocatalytic activity for water splitting,but also shows good energy storage and conversion ability.On the one hand,the overpotential of HER and OER in1 M KOH electrolyte is only 235 m V and 309 m V,showing high hydrogen and oxygen evolution activities.On the other hand,Co-CNTs@Ni S₂ electrode,as a supercapacitor,has an ultra-high specific capacitance of 1749 F g^-1 at a current density of 1 A g^-1.Under the high current density of 20 A g^-1,the capacity retention rate after 3000 cycles is 83.3%,showing good cycle stability.This work embodies the advanced concept of efficiently converting chemical energy into electric energy and clean gas（H₂）.