Ethyl viologen-functionalized reduced graphene oxide composites for asymmetric ionic liquid-based supercapacitors

The development of pseudocapacitive materials matching ionic liquid (IL) electrolytes can significantly enhance the performance of supercapacitors (SCs). Herein we report an ethyl viologen-functionalized reduced graphene oxide composite (EV-RGO) synthesized by one-step hydrothermal method. In EV-RGO, the ethyl viologen cations are anchored on the RGO sheets through electrostatic interactions, pi-pi stacking interactions, and cation-pi interactions, which makes EV-RGO as an electrode material more stable and reversible during charging and discharging. Meanwhile, the viologen cations with ethyl groups can better function as a spacer to suppress effectively the stacking of RGO sheets and expand their interlayer spacing. In 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF(4)) IL electrolyte, the electrochemical performance of the composite is enhanced due to synergic contributions from electric double-layer capacitance and pseudocapacitance. The pseudocapacitance mechanism is also supported by the results of XPS data. The specific capacitance of the EV-RGO as a negative electrode material for SCs reaches to 222.7 F g(-1) at a current density of 0.5 A g(-1). An asymmetric SC device (EVRGO//AC ASC) exhibits an energy density of 64.1 Wh kg(-1) at a power density of 888 W kg(-1). This work offers an advanced strategy for the fabrication of high-performance SCs using organic molecule-modified graphene composites.