Fabrication Of Polydopamine-derived Carbonaceous Composite Materials And Their Electrochemical Energy-storage Performance

Supercapacitors as a new type of electrochemical energy storage device with long cycle life and fast charge and discharge have attracted the attention of researchers.Electrodes are important components of supercapacitors,and electrode materials could determine the performance for supercapacitors.Among these electrode materials,carbon materials exhibit high power density and excellent cycle stability,but their specific capacitance is low;metal compounds,small organic molecules and conductive polymer materials have high specific capacitance,however,their conductivity is poor that could result in poor cycle stability and rate performance.Therefore,the researchers focus on these projects that carbon materials and other materials combine with each other to form novel composite materials with high specific capacitance,good cycle stability and rate performance.In this dissertation,different morphological structures are synthesised via biomass-derived electrode materials,and polydopamine-derived carbonaceous materials that combine with metal oxides and organic molecules.Furthermore,the excellent positive and negative electrode materials are reasonably designed and assembled into an asymmetric supercapacitor with a wide cell voltage in the aqueous electrolyte to achieve high energy density.The main contents are as follows:?1?9,10-Phenanthrenequinone-functionalized N-doped hollow carbon spheres?NHCSs/PQ?were synthesized,in which the NHCSs with high specific surface area and plentiful porosity were used as substrate,while the PQ molecules were used to realize the surface functionalization.The excellent electrical conductivity,plentiful porosity and the thin shell of NHCSs facilitated electron transportation and electrolyte ion diffusion.Moreover,the surface redox reactions of PQ molecules result in an outstanding electrochemical capacitive performance.In the three-electrode system,the PQ-functionalized NHCSs electrodes exhibited a larger specific capacitance(as high as 252 F g^-11 at 1 A g^-1)and excellent rate capability(80.8%capacitance retention at 30 A g^-1)in H₂SO₄ electrolyte solutions.Meanwhile,in order to match the capacitivebehaviorsofNHCSs/PQinthetwo-electrodesystems,NPCs/anthraquinone?NPCs/AQ?were also prepared.An asymmetric supercapacitor device?ASC?was assembled successfully by employing the NPCs/AQ as positive electrode and the NPCs/AQ as negative electrodes,respectively.More importantly,the device exhibited energy density of 8.34 Wh kg^-11 along with power density of 600W kg^-11 in aqueous electrolyte solution.?2?The bimetallic?Fe,Zn?hydroxide is synthesized through a one-step hydrothermal method,and dopamine is coated on the surface of them in an alkaline solution.Through the subsequent thermal treatment,the flower-like Fe₂O₃@C composite is formed by transforming the hydroxide precursor into its ferric oxides.The sheet-like composite material?MnCo₂O₄@C?could be obtained via the same method.Electrochemical measurements show that the Fe₂O₃@C and MnCo₂O₄@C electrodes achieve specific capacitances of 240 and 313 F g^-11 at 1 A g^-11 in potential windows of 0.85 V?-1.05^-0.3V?and 0.6 V?0⁰.6V?,respectively.To evaluate further the capacitive performance of Fe₂O₃@C composites in a full cell set-up,the as-constructed Fe₂O₃@C//MnCo₂O₄@C asymmetric supercapacitor?ASC?can deliver high energy density(16.1 Wh kg^-1)at the power density of 0.81 kW kg^-11 in 2 M KOH electrolyte.?3?The raisin is used as carbon sources and hierarchical porous honeycomb-like carbon materials?HPC?are prepared via high temperature carbonization and next activation.The prepared material HPC-2 has a high specific surface area(2667.6 m² g^-1)and exhibits excellent electrochemical performance due to more micropores and oxygen functional groups.As a result,HPC-2 electrode was tested in a three-electrode system,the specific capacitance of HPC-2 is up to 400 F g^-1with current density of 1 A g^-1,and retains 78.4%at 100 A g^-11 in a 2 M KOH electrolyte,which shows an excellent rate capability.To match with the HPC-2negative material,the flower-like NiO is used as positive electrode to assemble the ASC.The energy density of NiO//HPC-2 ASC in the 2 M KOH electrolyte is 40.1 Wh kg^-11 along with the power density of 0.90 kW kg^-11 with a cell voltage of 1.8 V.