Microstructure Modulation And Oxygen Vacancy Creation For Enhancing The Capacitive Performance Of Mo、Bi Based Electrode Materials

Mo and Bi-based metal oxide electrode materials based on the pseudocapacitor energy storage mechanism have high theoretical specific capacity,are very promising electrode materials.However,the poor electrical conductivity of metal oxides and the lack of cyclic stability due to rapid redox processes have limited their large-scale application.Therefore,researchers have addressed these issues in the following ways:（1）Structural design:restructure of materials to increase the specific surface area;（2）Composite with other carbon-based materials;（3）Introduction of oxygen vacancies to further enhance the intrinsic electrical conductivity and electrochemical activity of metal oxides.（4）Improve the crystallinity of the material and increase the charge transfer efficiency of the electrode material.In our work,oxygen vacancy-rich single-crystal Mo O₃ nanoribbons prepared by one-step hydrothermal method,and silver-ear-shaped Bi₂O₃ and plate-like Bi₂O₂CO₃ negative electrode materials were prepared by introducing water and NH₄HCO₃,respectively,in a solvothermal process,finally achieves the construction of oxygen-rich vacancies and improving the capacitive performance and stability of negative electrode materials.Asymmetric supercapacitor devices with high energy density and high stability were designed and constructed.The research contents of this paper are as follows:（1）Construction of oxygen vacancy-rich single-crystal Mo O_3-x nanobelt and asymmetric device performance evaluationOxygen vacancy-enriched Mo O_3-x nanobelts have been successfully synthesized via a simple one-step hydrothermal.The SEM and TEM shows that the Mo O_3-x sample is band-like structure and single crystal properties.Such enlarged interlayer spacing could increase the exposed metal atoms and promote the electron transfer,and thus guarantees the remarkable capacitance.Simultaneously,the enlarged interlayer spacing could weak the Van der Waals forces between layers and thus enhance the adsorption performance.Electrochemical evaluation reveals that the Mo O_3-x exhibit a high reversible capacitance of 912.5 F g^-1.The assembled Mo O_3-x//AC device exhibited an energy density of 22.5 Wh Kg^-1 at high power density of 5914.28 W Kg^-1.（2）Trace water to enhance the capacity of Bi₂O₃ via morphology modulation and oxygen vacancy creationConstruct oxygen vacancy enriched Bi₂O₃ with high electrochemical performance via addition of trace water into the solvothermal system.Due to the assembly of massive ultrathin nanosheets,tremella-shaped Bi₂O₃ is architected with more electrochemical active sites exposed and the porous structure guarantees the fast electrolyte permeation.The electrochemical results demonstrate the optimal tremella-shaped Bi₂O₃ delivers a high specific capacity of 889 F g^-1 at current density of 1 A g^-1,which is closed to the theoretical value.Remarkable cycle stability is also displayed with about 70%initial capacitance retained after 2000 cycles measurement.High-rate performance and long-term cycling stability are also realized because of the increased conductivity and crystalline.In addition to this,the assembly of Bi₂O₃ with AC into an asymmetric supercapacitor exhibits high energy density(40.8 Wh kg^-1,798W kg^-1),good multiplicative capability and scalable stability.（3）NH₄HCO₃ in situ water-regulated microstructure and construction of oxygen vacancies to improve the capacitive performance and stability of Bi₂O₂CO₃In situ water generated by NH₄HCO₃ decomposition during solvent heat for Bi₂O₂CO₃ microstructure modulation and oxygen vacancy creation.Revealing the mechanism of in situ water regulation of Bi₂O₂CO₃ microstructure by NH₄HCO₃through the addition of different carbonates.Due to the abundance of OH·in an alcohol-heated environment promoting the double hydrolysis of NH₄HCO₃,NH₃ produced during the reaction effectively avoids the accumulation of ammonium bicarbonate nanoplates.The Bi₂O₂CO₃ obtained by introducing NH₄HCO₃ is uniform in size,high crystallinity and abundant oxygen vacancies.At the same time,the trace water produced by hydrolysis can form abundant oxygen vacancies on the surface of Bi₂O₂CO₃.The electrochemical results demonstrate the Bi₂O₂CO₃exhibits high electrical capacity(720F g^-1,1 A g^-1)and stability（85%,5000）.This indicates that high-rate performance and long-term cycling stability due to increased conductivity and crystallinity.In addition to,the assembly of Bi₂O₂CO₃with hollow Ni Co-LDH into an asymmetric supercapacitor exhibits high energy density(45.76 Wh kg^-1).