| Phosphorus resources are abundant in reserves,but they are mostly used as fertilizers resuting in their low added value.Black phosphorus(BP),as an isotope of phosphorus,has graphite-like layered structure and is a semiconductor material with adjustable band gap.Monolayer BP,also known as phosphene,has graphene-like two-dimensional pleated structure,high carrier mobility and large specific surface.Therefore,phosphene exhibits excellent photoelectric,electrochemical and photocatalytic properties.But at present,the price of BP is very high,and phosphene is more expensive.The main reason is that the yield of BP prepared by chemical vapor deposition(CVD)is still very low.On the other hand,it is not suitable for large-scale preparation,which has become the key problem of the development of BP and its related technologies.Only by deeply exploring the mechanism and technological factors of BP-preparation can we find a way out for its development.It is not easy to exfoliate BP into thin phosphene for further application.At present,people try to exfoliate BP,but find it very difficult to carry out,and more difficult than that of graphite.The exfoliating experiments in this paper show that only 10%of the products with less than 10 layers of BP can be obtained through ultrasound liquid phase exfoliation or wet ball milling exfoliation.Most of the exfoliating products(about 80%)belong to multilayer BP(MBP).In view of the above situation,this article will further study the growth mechanism and influencing factors during the preparation of BP by CVD method,explore the exfoliating mechanism,pay more attention to MBP and systematically study the modification,composite and their electrochemical capacitance performance,as well as explore the application path of BP.First principles calculation method is used to understand the micromechanism of electrochemical capacitance improvement of modified MBP and its composites.The main contents of this paper are as follows:(1)The influencing factors and mechanism of BP in preparation and exfoliating are explored.Based on Schaffer's chemical vapor transport equation,the corresponding reaction equation of BP is established.In each temperature stage of BP growth,the existing form and state,position and function,formation and transformation mechanism of each substance are described in detail.The key temperature stages of the formation and transformation of nucleating agent and its precursors are defined.The influence and mechanism of temperature distribution in muffle furnace and the size of quartz tube on BP synthesis are also investigated.The study will provide a basis for the controllable and efficient synthesis of BP.As a result,the synthesis time of BP can be reduced from 24 hours to 12 hours.Furthermore,ultrasound liquid phase exfoliation and wet ball milling exfoliation are used to exfoliate BP,respectively.The effects of the ratio of BP to solvent and the type of solvent on the exfoliating effect are investigated for different exfoliating methods;the exfoliating mechanism of BP was explained by thermodynamic mixing function theory and molecular dynamics theory of the interaction between organic solvent and BP.The study will provide parameterization and theoretical guidance for the exfoliating of BP.(2)The preparation mechanism and capacitance performance of modified BP and its composites are explored.Firstly,based on water-bath ultrasonic method and wet ball milling method,BP is modified by saturated NaOH for its etching reaction to prepare MBP with rough surface and more active sites.It is found that the electrochemical capacity of hydroxylated MBP based on ultrasonic method is 70%higher than that of primeval BP.The hydroxylated MBP prepared by wet ball milling method shows better electrochemical cycling stability.It is also suitable as lamellar carrier because of its uniform size and rough surface morphology in micron scale.Then,using solvothermal method with anhydrous and mild temperature,Ni2P/MBP composite is successfully prepared through Ni2P nanoparticles in-situ growing on MBP by controlling the molar ratio of Ni to P.The electrochemical test shows that capacity of the composite is up to 1215 F/g.Based on the above methods,the bimetallic phosphide NixCoyP/MBP composite is prepared by introducing Co salt into the precursor system of Ni2P/MBP preparation.The composite has amorphous and in-situ dispersed flocculent structure exhibiting good electrochemical rate performance and cyclic stability.In addition,based on the idea of in-situ composite,the surface activity and lamellar carrier properties of hydroxylated modified MBP prepared by ball milling,polypyrrole and multilayer BP composites(PPy/MBP)and polyaniline and multilayer BP composites(PANI/MBP)are synthesized by chemical in-situ polymerization at low temperature.The electrochemical capacitance perfomance of the composites are investigated.And the results show that the capacity of PPy/MBP is 515 F/g,which is 70%higher than that of pure PPy;the capacity of PANI/MBP is 962 F/g,which is three times higher than that of pure PANI.In summary,The electrochemical capacitance performance of the two composites is better than that of their monomer.The mechanism analysis shows that the effective improvement is due to the hydroxylation modification of MBP.In addition to the dispersing effect of the lamellar carrier on the conductive polymer,the defective P atoms and hydroxyl groups on the surface of MBP can form P-C bonds and hydrogen bonds with the chain-end C atoms and N-H groups in the conductive polymer,respectively.These two bonds are beneficial to the in-situ bonding between the conductive polymer and BP.In the study of PPy/MBP composites,the existence of BP and the in-situ coating relationship between BP and PPy were confirmed by reducing the dosage of pyrrole.The "durian peel" morphology and nanostructure of PANI/MBP contribute to its better electrochemical capacitance performance.(3)The micro-mechanism and electrochemical capacitance performance of hydroxylated MBP and its composites are analyzed by first principles method.The configurations of Ni,Co and C atom-doped BP,P-doped Ni2P and configurations of hydroxyl(-OH),pyrrole(Py)and aniline(Ani)functional group-adsorpted BP are constructed respectively.The band structure,density of states and population distribution of the configurations are simulated and analyzed by first principles calculations.The results show that the changes of energy band and density of states caused by atom doping or functional group adsorption contribute to the increase of materials conductivity.Population distribution analysis shows that atom doping or functional group adsorption contribute to can help the electrons in the matrix migrate to the surface of the doped atoms or functional groups and improve the surface activity of the material.The study will provide theoretical support for electrochemical capacitance performance of relative materials.There are 136 figures,14 tables and 287 references in this paper. |
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