CVT Preparation Mechanism And Surface Modification Of Black Phosphorus And Electrocatalytic Performance Of It Compounded With Carbon Materials

As an emerging two-dimensional material,black phosphorus（BP）has received extensive attention from researchers because of its layered structure and excellent electrical properties.Although phosphorus is abundant on the earth,BP,as an allotrope of phosphorus,has a high preparation-cost,which leads to the high price,about 7000 RMB·g^-1.Therefore,the preparation and mechanism of BP has been a hot issue.In order to effectively reduce the cost,a systematic study on preparing BP is conducted by the chemical vapor transport（CVT）method.In this paper,the nucleation mechanism of BP is firstly analyzed,including the formation of the nucleation agent and the relationship between the nucleation agent and BP.Meantime,the best process-parameters of CVT are explored and the preparation time is effectively reduced,under the condition of ensuring the quality and yield of the product.Additionally,through a simple probe-assisted ultrasonic liquid phase exfoliation method,the functionalized BP nanosheets are obtained,which exhibit a better electrocatalytic performance.In this paper,the in-situ growth method is used to grow porous carbon structures with different morphologies on the functionalized BP nanosheets,to explore a new and effective method for the preparation of BP-based composites.The electron mobility of BP nanosheets is 220 cm²·V^-1·s^-1 and there are many active sites on the surface of BP,as a consequence,they are more suitable for application of electrocatalysis.However,the research on it is relatively new.Consequently,the prepared samples are tested for electrocatalytic performance to provide basic research.The main research contents of the full text are as follows:（1）Using the reagents（RP,Sn,and I₂）as raw materials,the orthorhombic BP single crystals,with the purity of 98%and the yield of 90%,are fabricated by the CVT method.Compared with the existing preparation time,the optimized preparation time is greatly shortened to 1035 min.Meanwhile,based on the principle of thermodynamics,the enthalpy and entropy changes of Sn₂₄P_19.3I₈ are calculated to explain theoretically the generation of Sn₂₄P_19.3I₈ in the system of RP/Sn/I₂.And from the perspective of kinetics and the analysis of HRTEM,the structural relationship between Sn₂₄P_19.3I₈ and BP is found.On the basis of the above,it is certain that Sn₂₄P_19.3I₈ is indeed a nucleation agent to induce the growth of BP.Moreover,through designing auxiliary experiments,we systematically observe the morphology of the product in each step and expound the preparation mechanism of BP in depth.And the corresponding characterization of BP is carried out.（2）Using succinic acid（SA）or ascorbic acid（L-AA）as an auxiliary and N,N-dimethylformamide（DMF）as the solvent,a simple probe-assisted ultrasonic liquid phase exfoliation method is used to obtain a series of functionalized BP nanosheets with different weight ratios.The samples are tested for electrocatalytic hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.At a current density of 10 m A·cm^-2,the overpotentials for OER of SA-BP-1:3 and L-AA-BP-1:1 are 369.8m V and 459.5 m V,respectively,and the overpotentials for HER of them are 235 m V and 224 m V,respectively.Compared with the electrocatalytic performance of pure BP nanosheets,that of the functionalized BP nanosheets has been effectively improved.Furthermore,the electrocatalytic cycle stabilities and long-term stabilities of the samples are also effectively improved.（3）Using functionalized black phosphorous nanosheets as the substrate,porous carbon structures with different morphologies are generated by the in-situ growth method to obtain the composite,BP nanosheets/porous carbon.The samples are tested for HER and OER.At the current density of 10 m A·cm^-2,the overpotentials for OER of PVP-BP-PC-1 and PVP-BP-PC-2 are 433 m V and 430.8 m V,respectively,and the overpotentials for HER of them are 190 m V and 238 m V,respectively.Compared with the electrocatalytic performance of the sample prepared by mechanical mixing,that of the samples prepared by the in-situ growth method are significantly improved.In addition,the electrocatalytic cycle stability and long-term stability of the samples are also effectively enhanced.