Study On Synthesis And Performance Of Spherical Structure Metal Oxides For Energy Materials

The systhesis and application of spherical structure metal oxides energy materials as the hot topics have attracted enormous interests due to their high specific surface area,structure stability,facile synthesis and excellent electrochemical preoperties.St?ber method as a kind of traditional and classical way has been exploited for the synthesis of materials.A series of metal oxides?i.e.TiO₂ hollow spheres,Zn₂Ti₃O₈ hollow spheres,Co₃O₄@TiO₂@C yolk-shell spheres,Fe₃O₄@TiO₂@C yolk-shell spheres,Co₃O₄@RGO compounds and SiO₂@Mn-based compounds core-shell spheres?have been successfully synthesized,which are applied for the photoanodes of dye-sensitized solar cells?DSSCs?or anodes of lithium ion batteries?LIBs?.In addition,carbon spheres as templates are used to synthesize the upconversion NaxGdFyOz:Yb/Er hollow spheres for the research of dye-sensitized solar cells.Photoelectric tests,charge-discharge tests,cyclic voltammetry and electrochemical impedance spectroscopy are performed to investigate the mechanisms of materials' electrochemical and photoelectrochemical reactions.Zinc ions have been embedded into the TiO₂ nanocrystals via ion exchange to form the different shell thicknesses of Zn₂Ti₃O₈ hollow spheres by using SiO₂ spheres as templates.When Zn₂Ti₃O₈ ternary oxides are evaluated as anode of LIBs,the batteries exhibit the superior cycling stability and rate performance.The delivered capacities of186.2 mAh g-1and 173.6 mAh g-1have been achieved after 100 and 200 cycles at a current density of 200 mA g-1.Co₃O₄@TiO₂@C yolk-shell spheres,Fe₃O₄@TiO₂@C yolk-shell spheres and Co₃O₄@RGO compounds are prepared via St?ber method.The results show that these composites clearly possess much better cycle stability and electrochemical performance after coating a layer of materials with stable electrochemical properties.This indicates that the outer layer can effectively inhibit and buffer volume expansion and crack of the internal metal oxide in the intercalation and deintercalation processes,and reduce the polarization of electrode,leading to the improvement of cycling stability.The SiO₂@ZnxMn₂O₄ core-shell spheres are synthesized via hydrothermal treatment and ion exchange.The results show that a portion of Zinc ions are not embedded into the MnCO₃ crystal lattice,which are formed ZnO nanoparticles in the ion exchange process.It is worth mentioning that the SiO₂@ZnxMn₂O₄ compositesexhibit good electrochemical performances on the basis of galvanostatic charge-discharge tests,the cyclic voltammetry and the electrochemical impedance test.SiO₂@SnO₂-MnCO₃ core-shell spheres are synthesized via one-step hydrothermal treatment.However,the electrochemical properties of materials are not so good.The shell thicknesses of TiO₂ hollow spheres are controlled via adjusting the amounts of TBOT.The PCE measurements show that the scatter effect of TiO₂ hollow spheres is obviously higher than that of TiO₂ nanoparticles.PEG-400 is a high viscosity dispersant,which is chosen to use as the dispersant of RGO and TiO₂ hollow spheres during the fabrication of photoanode.By this means,RGO can be introduced well into the photoanode to get the stable PCE.Additionally,the upconversion materials Nax GdFyOz:Yb/Er@TiO₂ hollow spheres have been introduced into the photoanode of DSSCs for the improvement of PCE due to the scatter effect and upconversion effect.