Synthesis Of Two-Dimensional Bismuthene And Its Application Exploration In Energy Storage And Conversion

Elemental two-dimensional materials show great promise in the next generation of electronic,optoelectronics,energy and other fields,even changing the rules of the game.Recently,due to its topological nontrivial state,surface plasmon resonance effect and special sodiation alloying structure,bismuthene has become a hot research object in the fields of energy and optoelectronics.However,bulk bismuth possesses much stronger interaction energy compared to the common elemental layered structure material,so the traditional"top-down"methods such as mechanical exfoliation and liquid phase exfoliation are difficult to effectively exfoliate the bulk bismuth into high-quality bismuthene nanosheets.At the same time,the energy storage mechanism of bismuth material is still questionable,and the performance improvement and structural design of new type photoelectric devices based on bismuthene are still remain blank.From these,a series of synthesis methods of bismuthene with high quality and high yield are developed to achieve high-quality bismuthnene nanosheets.Besides,the electrochemical sodium storage and the photoelectrochemical properties of bismuthene are explored.The main research results are summarized as follows:（1）A hydrothermal synthesis method is developed to achieve bismuthene nanosheets with the universal thickness of 5nm by controlling concentration of Bi³⁺during the reaction process.The synthesized bismuthene nanosheets are vertical grew uniformly and densely on the surface of aluminum powders with a high yield rate of 68%.And the as-prepared bismuthene nanosheets are all corresponding to theβ-Bi.（2）The structure and phase transitions of layered bismuth（few-layer bismuth nanosheets）have been disclosed during Na⁺intercalation and alloying processes by using in situ transmission electron microscopy.Multistep phase transitions from Bi→Na Bi→c-Na₃Bi（cubic）→h-Na₃Bi（hexagonal）are clearly identified,during which the Na⁺migration from interlayer to in-plane evokes the structure transition from ABCABC stacking type of c-Na₃Bi to ABABAB stacking type of h-Na₃Bi.It is found that the metastable c-Na₃Bi devotes to buffer the dramatic structure changes from thermodynamic stable h-Na₃Bi,which unveils the origin of volume expansion for bismuth and has important consequences for 2D in-plane structure.As the lateral ductility can efficiently alleviate the in-plane mechanical strain caused by the Na⁺migration,the few-layer bismuth nanosheet exhibits a potential cyclability for Na-ion batteries.（3）The surface oxidation process of bismuthene nanosheets synthesized by hydrothermal method is carried out by the Bi（012）plane which will in situ transform intoβ-Bi₂O₃（200）plane and only cause small interlayer lattice distortion.And the surface photovoltage experiments shows that this surface oxidation process is reversible under certain conditions.Taking advantage of this phenomenon,a novel P-type photoelectrochemical tandem cell is designed based on bismuthene nanosheets covered byβ-Bi₂O₃ on its surface.The photoanode and photocathode,simultaneously integrated on the same FTO electrode,are carried out by a simple polarization process of oxidation and reduction on the two electrodes respectively,which process under simulated sunlight irradiation and a certain bias condition.The PEC tandem system can achieve a photocurrent density of 210 n A cm^-2 without bias.In addition,the whole system exhibits good stability after polarization process,and the photocurrent density remains after 12 hours.