Improving supercapacitor performance of alkylated graphene nanosheets via partial fluorination on their alkyl chains

Abstract

Redox-active graphene materials are highly desirable for the production of high performance supercapacitors. Following our previous work that found that alkylated graphene nanosheets are a new kind of such material, we report here that the simple replacement of alkyl side chains with partially fluorinated alkyl chains further improves their capacitive electrode performance. In this work, one partially fluorinated graphene material (pFAG) was prepared by the reaction of KOH-pretreated graphene oxide with 2-perfluorohexylethyl bromide in the presence of a phase transfer catalyst. Compared with the graphene material modified with octyl side chains (AG), pFAG possesses a larger amount of residual oxygen functionalities, which is favorable to endow the material with a redox-active nature and achieve a larger faradaic capacitance. Moreover, pFAG presented a special self-assembly behavior and formed continuous and large plate-like objects in the solid state. Finally, a supercapacitor electrode was fabricated with pFAG and its performance was compared with the previously reported AG-based electrode in detail. It was found that the pFAG electrode has a much better capacitive performance than that based on AG (218.3 vs. 160.0 F g⁻¹ at a scan rate of 100 mV s⁻¹ by cyclic voltammetry, and 187.0 vs. 118.8 F g⁻¹ at a current density of 3 A g⁻¹ by galvanostatic charge/discharge method). When charge/discharge was carried out at 1 A g⁻¹, the specific capacitance of pFAG-based electrode reached 388.0 F g⁻¹, among the highest values of reported graphene-based electrodes. Furthermore, pFAG electrodes exhibited a good cycling stability. All these demonstrate graphene nanosheets modified with partially fluorinated alkyl chains would be a good way to achieve high performance redox-active electrode materials.