Syntheses And Properties Of Cobalt Compound/carbon Materials Based On Metal-Organic Frameworks And Antimony Halide Complex

Meta-organic frameworks?MOFs?are periodic networks self-assembled by metal ions and organic ligands via coordination bonds.MOFs possess high surface areas and diverse structures,they have a wide application in chemistry,material and medical science,et al.MOFs have been demonstrated as templates to create carbon nanocomposites via calcination.And the microstructures of the carbon nanocomposites obtained by this method can be controlled by MOF precursors,in which the carbon conductive network provides a good transport channel for electrons and substances.In this thesis,cobalt compound/carbon nanocomposites have been synthesized based on the MOFs of cheap cobalt metal as precursors by calcining method,and they were characterized by powder X-ray diffraction?XRD?,infrared spectrometry?IR?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,energy-dispersive X-ray spectra?EDS?,selected area electron diffraction?SAED?,X-ray photoelectron spectroscopy?XPS?and Brunauer-Emmett-Teller?BET?,and so on.Their electrochemical properties such as electrocatalysis for oxygen evolution reaction?OER?and electrode material in supercapacitors were further investigated.The main contents in the thesis are summarized as follows:In the first chapter,it was summarized the basic concepts,research significancesand developments for MOFs,OER and supercapacitors.Inthesecondchapter,MOFprecursor,Co?H₂L?₂?H₂O?₂·2DMF?H₃L=2-thiobarbituric acid,DMF=N,N-dimethylformamide?was prepared by ultrasonication at room temperature.Co₉S₈@CoS@CoO@C nanoparticles?NPs?of5²0 nm were synthesized by annealing the MOF precursor.The Co₉S₈@CoS@CoO@C NPs exhibit excellent electrocatalytic activity for oxygen evolution reaction?OER?with a lower overpotential than RuO₂?0.37 V?and Pt NPs?0.60 V?,which is associated with its heterojunction structure,in which the strong electron coupling interactions between Co₉S₈,CoS,CoO and C give rise to a superior synergistic effect.The interconnected amorphous carbon not only affords conducting channel for electron transfer,but also anchors the active Co compounds to avoid aggregation.Furthermore,the cobalt compounds were the active species in the sample during the OER process,they were converted into CoOOH and Co?OH?₂ in the KOH electrolyte,and the S elements in the sample entered the solution.The Co₉S₈@CoS@CoO@C NPs can exhibit the best OER activity with minimum overpotential?0.028 V?to afford a stable OER current after activation in KOH aqueous solution.The sample also showed obvious photoresponse to visible light irradiation with enhanced OER current and lowered onset potential,which was probably associated with the semiconducting characteristics of the spin-polarized CoO and the quantum confinement effect of the nanoparticles.In the third chapter,MOF precursor,Co₄?phen?₄Cl₈?phen=1,10-phenanthroline?was prepared solvothermally.Based on the MOF precursor,Cl/O doped C/CoO material?C/CoO-200?was synthesized by a one-step calcining method at a low temperature of200?.In C/CoO-200,CoO nanoparticles with an average size of 25 nm were linked by carbon matrix into particles with the diameter of 200 nm¹?m.The sample possessed a large amount of carbon,which was from the organic ligand?the decomposition of phen?,then the atomic percentage of CoO in the sample was very low?CoO:1.9%;C:86.8%?.However,it still exhibited a large specific capacitance of 1052 F g^-11 at 0.5 A g^-1in 2 M KOH electrolyte with a 79.6%capacitance retention at 10 A g^-1.After successive etched in acid,Cl/O doped carbon nanoparticles were obtained.C-300 was composed by individual nanoparticles with size of 100-500 nm,it showed a specific capacitance of207 and 164 F g^-1 in 2 M KOH at a current density of 0.5 and 1 A g^-1,respectively,which was comparable to the commercial activated carbon?AC?(199 and 179 F g^-1 for AC at 0.5 and 1 A g^-1,respectively).An asymmetric supercapacitor based on the positive electrode of C/CoO-200 and the negative electrode of C-300 exhibited a stable performance with a 61%retention of specific capacitance after 10000charging-discharging cycles at 1.5 A g^-1.In the fourth chapter,using an organoamine,2,5-bis?1-imidazoly?pyridine?L?,a novel inorganic-organic hybrid material based on antimony halide formulated as[?CH₃CH₂?₂L][?Sb₄I₈Cl₈?_0.5]?1?was in situ synthesized via solvothermal technique and it was characterized by single-crystal X-ray diffraction.During the synthesis,the organoamine,L was in-situ transformed into the imidazolium ion,[?CH₃CH₂?₂L]²⁺.In compound 1,four Sb?III?ions are linked by two?₃-I^-and four?₂-I^-ligands into a?Sb₄I₈Cl₈?^4-unit,in which the eight Cl^-ions and two I^-ions act as the terminal ligands.And the uncoordinated[?CH₃CH₂?₂L]²⁺organoamine moieties are linked with the?Sb₄I₈Cl₈?^4-clusters via H bonds into three-dimensional?3D?supramolecular architecture.The band structure calculation shows that the compound has an indirect band gap of 2.253 eV.