Controllable synthesis of graphene scrolls and their performance for supercapacitors

A graphene scroll (GSC) is a new type of graphene-derivative material, that has widely attracted attention. However, the controllable preparation of GSCs is a major factor influencing their development and application. In this work, sodium citrate (SC) was added to a graphene oxide (GO) aqueous suspension and GSCs were controllably prepared on a large-scale by a cold quenching method. The results show that the number of scroll layers and the curling degree of the GSCs could be controlled by the quantity of SC added. The diameter of the GSCs increased when SC was added. Compared to the GSC without SC (265 nm), the average diameter of GSC(SC-40) (obtained by adding 40 mg SC to 100 mL GO solution (1 mg mL^-1)) is 491 nm. When excessive SC was added, such as 100 mg, the average diameter reached 679 nm. Moreover, these GSCs were used as a supercapacitor electrode material and the electrochemical performance was tested. The specific capacitance of GSC(SC-40) (178 F g^-1) is higher than that of the GSC without SC (107 F g^-1) at the same current density of 1.0 A g^-1. However, when a larger quantity of SC was added, the specific capacitance of the GSCs decreased. So, the number of scroll layers and the curling degree of the GSCs have a significant effect on the electrochemical properties of the supercapacitor.