Fabrication Of Several Organic Molecular Electrodes And Their Energy Storage Performance

With the characteristics of safely delivering high power density and extremely long cycle life,supercapacitors have an indispensable position in the field of energy storage.However,the large energy density gap between supercapacitors and the ion batteries used in actual production makes them much limited in the applications of new energy vehicles,load balancing systems for intermittent renewable energy sources,and portable devices.Therefore,while maintaining the inherent advantages of supercapacitors,increasing their energy density is still a pressing issue in the current development of supercapacitor applications.In recent years,electroactive small molecules screened from nature or artificially green synthesized can achieve multi-electron reversible Faraday reactions at low molecular weights,which results in high theoretical specific capacitance and excellent energy storage potential.More importantly,organic molecules can introduce specific functional groups into the molecular structure through flexible and convenient organic reactions to tune and design their electrochemical properties.In this dissertation,indole or polyphenol organic molecules with electrochemical activity were selected and modified on the reduced graphene oxide surface（r GO）by a non-covalent strategy to prepare organic molecular electrodes with excellent electrochemical properties.In addition,a new polymer was synthesized from piperazines and anthraquinones organic molecules by the Schiff base reaction.The prepared polymer is anchored on the r GO surface to prepare an organic molecular electrode,by which the electrochemical properties of the polymer are released.Asymmetric supercapacitors（ASC）with high energy storage performance are assembled through rational matching between positive and negative electrodes,and the electrochemical energy storage performance of ASC is analyzed.The following is a summary of main research contents:（1）The five-membered heterocyclic 5-hydroxy indole（HIN）molecule was modified on r GO as an organic pseudocapacitive active donor to prepare an organic molecular electrode（HIN@r GO）.In the three-electrode test system,the Faraday reaction of HIN@r GO occurs in a relatively positive potential range.The optimized electrode（HIN@r GO-0.5）possesses a specific capacitance of 519.5 F g^-1 at a sweep rate of 5 m V s^-1 and a capacitance retention of 85.6%when the sweep rate is increased to 100 m V s^-1.To match the prepared organic molecular electrodes,MXene（Ti₃C₂T_x）was prepared as the negative electrode.The asymmetric supercapacitor is assembled with HIN@r GO-0.5 and Ti₃C₂T_x as positive and negative electrodes（HIN@r GO-0.5//Ti₃C₂T_x ASC）,respectively.The obtained ASC device can have a potential window of 1.6 V in 1 mol L^-1 H₂SO₄ electrolyte and provide an energy density of 32.5 Wh kg^-1 at 640 W kg^-1 power.Moreover,ASC has excellent cycling stability（90.5%capacitance retention after 10000 cycles）.Two devices connected in series can light up to 58 LEDs,demonstrating the potential for practical applications.（2）The non-flavonoid polyphenolic resveratrol molecules（RE）were modified on the surface of r GO to prepare novel organic molecular electrodes（RE@r GO）.The RE molecules possess multiple phenolic hydroxyl groups,which can realize multi-electron Faraday reactions for the excellent performance of organic molecular electrodes.The optimized electrode RE@r GO-0.8 has a high specific capacitance of367.9 F g^-1 at 5 m V s^-1and excellent capacitance retention(81.6%capacitance retention even at a scan rate of 100 m V s^-1).In order to verify the potential of organic electrodes for practical applications,another organic molecular electrode（BAQ/r GO-0.3）was prepared as a negative electrode.The ASC component（BAQ/r GO-0.3//RE@r GO-0.8）are assembled by using RE@r GO-0.8 as the positive electrode and BAQ/r GO as the negative electrode.The prepared ASC can provide an energy density of 22.8 Wh kg^-1 at a power density of 527 W kg^-1.Two ASCs connected in series can electrically illuminate 43 red LEDs.（3）A new organic pseudocapacitive active component（poly-1,4-piperazinedicarboxaldehyd-2,6-diaminoanthraquinone,PDP）was synthesized by combining an electrochemically active molecule and a high electron cloud density molecule to create a Faraday reaction unit with a high electron cloud density.Then,the organic molecular electrode（PDP@r GO）was prepared by anchoring the PDP on the r GO surface.The optimized electrode PDP@r GO-1 has a high specific capacitance of 964.8 F g^-1 at 5 m V s^-1 and a capacitance retention of78.7%even at a scan rate of 100 m V s^-1.The ASC devices（PDP@r GO-1//LGH）were assembled by porous oxygen-rich graphene hydrogel（LGH）as the positive electrode and PDP@r GO-1 as the negative electrode.The component delivers an energy density of 27.9 Wh kg^-1 at a power density of 532 W kg^-1.Two components（in series）can light up 54 red LEDs.