New Organic Molecule Electrodes And Their Energy Storage Properties

Supercapacitors,as a new and green energy storage unit,provid high power and suitable energy density,and play an important role in many fields.The energy density of the supercapacitor is relatively low in comparison with the batteries,which severely limits its practical application.Therefore,it is still a challenge to increase the energy density without losing its high power.Organic molecule electrodes have been applied in various energy storage devices due to outstanding characteristics.Essentially,the organic molecule electrodes are a kind of composite electrodes that the organic molecules with desired structures and groups are modified on a conductive carbon scaffold viaπ-πinteraction or chemical bonds.The carbon scaffold is able to anchor the electrochemically active organic molecules on it and accordingly prevent them from migrating in the electrolyte solutions between the negative and positive electrodes,which generate shuttle effect to lead to energy lost inside the device.In addition,the organic molecule electrodes can not only store charges through redox reactions of groups on the molecular skeletons but also contribute electrical double layer capacitance to the whole electrode due to the surface electrochemical properties of conductive carbon substrates.However,available commercialized quinones（phenols）molecules are less in categories and insufficiently variable in the structure,and so they unable to meet the needs for developing supercapacitor.Therefore,the synthesis and design of new organic molecules with desired physical,chemical and electrochemical properties are an effective strategy for preparing organic molecule electrodes,which will provide broad material choice for the next generation of green energy storage system.In the thesis research,anhydride organic molecules are selected to synthesize the imide derivative with electrochemically active through organic chemical synthesis strategy,and then anchor it onto the reduced graphene oxide surface by non-covalent strategy to form an organic molecular electrode with outstanding performance.In addition,the phenols organic molecules are chosen to modify them onto reduced graphene surface,and a new type of phenol organic molecular electrode is obtained.The positive and negative electrodes are reasonable matched to assemble the asymmetrical device（ASC）,and the electrochemical energy storage performance of ASC is studied.The main contents are as follows:（1）A new redox active organic molecule,naphthalene diimide derivative（NDI）,is synthesized through the condensation reaction for electrochemical energy storage,in which 1,4,5,8-naphthalenetetracarboxylic dianhydride and 4-aminophenol are used as skeleton and substituent,respectively.The NDI is acted as a guest molecule to non-covalently modify reduced graphene oxide（r GO）and form an organic molecular electrode.The resultant electrode exhibits outstanding performance under the three-electrode configuration,including specific capacitance(354 F g^-1 at 5 m V s^-1),cycling performance（87.2%after 8000 cycles）.Furthermore,the electrochemical behaviors of the OMEs are mainly controlled by surface reactions and pseudocapacitance contribution is up to 93%of the total capacity at 100 m V s^-1.In addition,a positive electrode（graphene hydrogel-2,6-Dihydroxynaphthalene:GH-DN）is formed by hydrothermal method.At last,an asymmetric device（GH-DN//r GO-NDI,ASC）is assembled and specific capacitance of 111.3 F g^-1 is reached.The power density is 0.6 KW kg^-1,the GH-DN//r GO-NDI ASC can deliver high energy density of 26.3 Wh kg^-1.Moreover,two ASC devices in series may be light 81 LEDs.（2）The polyhydric organic molecules（3,4,5-Trihydroxybenzamide,THBA）as a guest molecule decorate graphene hydrogel（GH）to form an organic molecular electrode.The THBA acts as a spacer to prevent GH sheet from aggregation and provides active center for organic molecular electrode.In the three-electrode configuration,the prepared GH-THBA presents a specific capacitance of 390.6 F g^-1 and has capacitance retention of73.7%even when the scanning rate increases from 5 to 100 m V s^-1.Furthermore,we synthesize an organic molecule 1,4,5,8-Naphthalenetetracarboxylic diimide（NDP）and immobilize it onto the r GO surface to form another OME（r GO-NDP）as the counter electrode.An all carbon asymmetric supercapacitor（GH-THBA//r GO-NDP,ASC）is constructed by using GH-THBA and r GO-NDP as positive and negative electrodes,respectively.The resultant device achieves capacitance of 70.8 F g^-1 and the power is 590W kg^-1,the energy density of GH-THBA//r GO-NDP delivers 14 Wh kg^-1.More importantly,the two asymmetric devices in series connection are able to light up 24 LED lights for 100 seconds.（3）This work reports a feasible method to fabricate a novel organic molecule electrode,in which the 3,4,9,10-perylenetetracarboxylic acid（PTCA）is immobilized on the surface of reduced graphene oxide（r GO₁）by using a non-covalent strategy.In the three electrode configuration,the specific capacitance for the PTCA/r GO₁electrode is422.7 F g^-1 at 10 m V s^-1.More importantly,it can retain 94.6%of the initial value at 100m V s^-1.This ultra-high rate capability could be put down to ultra-fast protonation/deprotonation electrochemical reaction based on the four carboxyl groups in PTCA.To further explore the practical performance of electrode materials,the asymmetric supercapacitor（PANI/r GO₂//PTCA/r GO₁）is constructed by using PTCA/r GO₁ and PANI/r GO₂ as the negative and positive electrode,respectively.The device（PANI/r GO₂//PTCA/r GO₁ ASC）reveals an outstanding energy storage capacity,which a power density reaches 520 W kg^-1,the PANI/r GO₂//PTCA/r GO₁ ASC have an energy density of 14 Wh kg^-1.