Electrochemical Energy Stoarge Of The Modified Carbon Electroactive Electrode Materials

Supercapacitors have the advantages of high power density,fast charge-discharge rate,long cycling life,and environment friendliness et al.Electrode materials have been considered to be the key factor that determine the overall performance of supercapacitors.Carbonaceous materials are widely used as the electrode materials for supercapacitors.Electrical double layer capacitance based on the ion adsorption-desorption has always been difficult to break through the bottleneck of low energy density.There are two strategies to modify the electroactive carbon materials:?i?carbonaceous materials as the modified component to composite with other active materials,?ii?the doping and modification for carbonaceous materials.In this work,the preparation and electrochemical performance of the modified carbon electroactive electrode material have been systematically studied.On one hand,modified polyaniline was synthesized by adding the conductive carbon quantum dots,which is to increase the specific capacitance and cycling stability of PANI.On the other hand,nitrogen doped carbon materials and boron,nitrogen co-doped carbon materials was fabricated.The improvement of specific capacitance of modified carbon materials was achieved by the introduction of the pseudocapacitance from the boron and nitrogen containing functional groups.The main contents and results are as follows.?1?Preparation and electrochemical performance of carbon quantum dots-polyaniline hybridModification of polyaniline?PANI?by carbon quantum dots?CQDs?:CQDs-PANI hybrid was fabricated as supercapacitor electroactive material by the photoelectrodepositing method,using carbon fiber as the substrate.PANI nanowires were grown vertically on carbon fiber to form an interconnected network structure.Meanwhile,CQDs was uniformly distributed in the interior and on the surface of well-established net-like PANI nanowires.High specific capacitance of 738.3 F g^-1 at 1.0 A g^-1 was obtained for CQDs-PANI compared to that of 432.5 F g^-1 for pure PANI.The capacitance retention after 1000 cycles of CQDs-PANI and PANI is 78.0%and 68.0%at 5.0 A g^-1,respectively.The distinct improvement of specific capacitance and cycle stability of PANI were ascribed to the incorporation of CQDs,which improved the conductivity and alleviated the volume change of the CQDs-PANI electrode during the charge/discharge process.In addition,a flexible symmetrical solid-state supercapacitor was constructed using CQDs-PANI electrode materials.The specific capacitance,energy and power density of the device were determined to be 169.2mF cm^-2,33.8?Wh cm^-22 and 0.3 mW cm^-2 at a potential window of 1.2 V and a current density of 1.0 mA cm^-2.?2?Preparation and electrochemical performance of polyaniline-derivated nitrogen doped carbon nanowiresNitrogen doped carbon?NDC?:NDC nanowires growing on carbon paper?CP?substrate were fabricated by high temperature carbonization of PANI nanowires,using PANI as the nitrogen source and carbon source.The NDC electroactive material exhibits a high specific capacitance of 404.0 F g^-1 at 1.0 A g^-1.The superior capacitance results from the good electron-donor properties of heterocyclic nitrogen distributed in the carbon skeleton and reversible redox reactivity of exocyclic nitrogen-containing functional groups at the edge of carbon skeleton.A low capacity decay of 22%indicates high rate capability when current density increases from 1.0 to 10 A g^-1.A high capacity retention ratio of 95.8%after 5000cycles at 10.0 A g^-1 presents good cycling stability.In addition,a symmetrical solid-state supercapacitor was constructed using NDC/CP electrode.The device delivers a specific capacitance of 187.1 F g^-1 at 1.0 A g^-1,an energy density of 66.54 Wh kg^-1 at the power density of 0.8 kW kg^-1,the capacity retention ratio of 94.1%after 5000 cycles at 5.0 A g^-1 and an output voltage of 1.6 V.?3?Preparation and electrochemical performance of porous boron,nitrogen co-doped carbon nanowiresPorous boron,nitrogen co-doped carbon?BNDC?:the BNDC nanowires supporting on carbon paper?CP?substrate were prepared by one-step high temperature carbonization method,using boric acid?H₃BO₃?as the boron source,PANI as the nitrogen source and carbon source.The polyaniline and boric acid?PANI-H₃BO₃?composite shows the close-packing nanowire structure with a diameter around 120 nm.The BNDC was formed through carbonization of PANI-H₃BO₃ intermediate.The BNDC shows nanowires-interconnected network structure with a diameter around 90 nm.The BNDC exhibits high specific capacitance of 504.0 F g^-11 at 1.0 A g^-1.The superior capacitance mainly results from the pseudocapacitance of boron and nitrogen containing functional groups,and the high surface area of 1068.9 m² g^-1 caused by porous structure also facilitates the increase of specific capacitance.BNDC showed the negligible capacitance decay after 5000 cycles at10.0 A g^-1,presenting good cycling stability.In addition,a symmetrical solid-state supercapacitor was constructed using BNDC/CP electrode.The device delivers a specific capacitance of 255.7 F g^-1 at 1.0 A g^-1,an energy density of 90.9 Wh kg^-1 at the power density of 0.8 kW kg^-1,the capacity retention ratio of 91.0%after 5000 cycles at 5.0 A g^-1 and an output voltage of 1.6 V.The BDNC supercapacitor exhibits comparable capacitance performance to the state-of-the-art carbon supercapacitor,showing promising application in energy storage devices.