Microwave synthesis of histidine-functionalized graphene quantum dots/Ni-Co LDH with flower ball structure for supercapacitor.

A flower ball-like histidine-functionalized graphene quantum dots/Ni-Co LDH (His-GQD/LDH) composite is synthesized via microwave method. The GQDs are uniformly interspersed on LDH surface and the radius of flower balls is approximately 200 nm. The synergistic effect of His-GQD and LDH can signally increase the specific surface areas and conductivity of the composite, thus endowing the composite high specific capacitance (1526 F g) and an admirable cycling stability (82.36% capacitance retention). Moreover, we have manufactured a supercapacitor employing His-GQD/LDH and active carbon (AC) as positive/negative electrodes. The device exhibits the maximum energy of 48.89 W h kg at 0.80 kW kg, as well as prominent cycling stability (91.13% capacitance retention). This work provides a practicle experimental method of synthesizing hybridizing histidine-functionalized carbon derivatives with LDH by microwave synthesis. Meanwhile, we are optimistic to believe that the electrode material can be extensively applied for supercapacitor because of its splendid electrochemical properties and facile synthesis.