Synthesis Of Two Dimensional Composites Via In Situ Collaborative Technology For Supercapacitors

As a new electrochemical energy storage device,supercapacitors?SCs?have received an increasing attention,due to their rapid charge and discharge rates,high power density,environmental friendly property and long cycling stability.However,the widespread applications of SCs are hindered by their intrinsically low energy density.The energy density is determined by the specific capacitance and the operating voltage of the devices.The focuses of this thesis is on the improvement of the specific capacitance of composites,which were prepared on two-dimensional layer?graphene or molybdenum sulfide?via in-situ collaborative technology.The electrochemical performance of the composites was modified through optimizing their nanostructure and adjusting the valence state of the element.The detail contents are as follows:At first,the nitrogen-doped hierarchical porous carbon?NHPC?material was successfully synthesized from a gelatin and graphene oxide composite via a combined solvation volatilization/nano-CaCO₃ template/KOH activation method.The obtained NHPC exhibits a large surface area(S_BET=1091 m² g^-1)as well as a combination of electrical double layer capacitance and pseudocapacitance behavior.NHPC shows a specific capacitance of 234 F g^-1 at 0.5 A g^-1 in a three-electrode system.Moreover,supercapacitor based on NHPC exhibits an excellent cycle life?retaining>98%after5000 cycles?and a high energy density up to 9.43 Wh kg^-1.Secondly,a series of polydopamine?PDA?modified reduced graphene oxide?rGO?/amino functionalized carbon nanotube?CNT-NH₂?aerogel composites?GCP?were synthesized via hydrothermal method on in situ collaborative technology.The GCP possess three dimensional cross-linked hierarchical porous structure and self-supported character.Moreover,it incorporates the advantages of 1D nanotube for effective charge transport,2D graphene nanosheet for fast ion transport and 3D cross-linked hierarchical porous substrate for mechanical stability and flexibility.Attributing to these characters,GCP electrode presents a high capacitance(176.2 F g^-1 at 0.5 A g^-1)in aqueous 6.0 M KOH electrolyte.Symmetric supercapacitor based on GCP electrodes exhibits a high energy density of 4.22 Wh kg^-1 and excellent cycling stability with 98.9%capacitance retention after 10,000 cycles.Furthermore,the supercapacitors show superior flexibility stability.The facile synthesis,promising electrochemical results and 3D hierarchical porous nanostructure of GCPs present potential for supercapacitor and other energy storage applications.Thirdly,different amount of polyaniline grafting on 4-aminophenyl functionalized molybdenum sulfide nanosheets?MoS₂-NH₂/PANI?were prepared by covalent bond reaction.The MoS₂-NH₂/PANI present sandwich structure and a certain proportion of molybdenum sulfide possess a high conductivity 1T phase.Moreover,it presents a high capacitance of 326.4 F g^-1 at 0.5 A g^-1 and a superior rate capacity with a retained 63.1%original capacity of 164.3 F g^-1 even at 1000 A g^-1 in three electrode system.The corresponding symmetric supercapacitor shows a good capacity rate and delivers an electrochemical cycling stability with 96.1%retention after 10 000 cycles.