ARTICLE pubs.acs.org/JPCC
Preparation of Highly Conductive Graphene Hydrogels for Fabricating Supercapacitors with High Rate Capability Li Zhang and Gaoquan Shi* Department of Chemistry, Tsinghua University, Beijing 100084, People’s Republic of China
bS Supporting Information ABSTRACT: Graphene hydrogels prepared via hydrothermal reduction of graphene oxide dispersions (GH-Hs) were further reduced with hydrazine (Hz) or hydroiodic acid (HI) to improve their conductivities. The chemically reduced graphene hydrogels possess high conductivities of 1.3 3.2 S m 1, which are 1 order of magnitude higher than that of a GH-H (0.3 S m 1). The supercapacitor based on the Hz-reduced GH-H exhibited a high specific capacitance of 220 F g 1 at 1 A g 1, and this capacitance can be maintained for 74% as the discharging current density was increased up to 100 A g 1. Furthermore, it showed high power density and long cycle life. The highperformances of this supercapacitor make it promising for high rate charge/discharge applications.
1. INTRODUCTION Graphene, a one-atom thick graphite sheet, is recognized as a promising carbon material for fabricating high-performance supercapacitors because of its low mass density, excellent electrical conductivity, and high specific surface area (SSA; ∼2630 m2 g 1, theoretical).1 6 Both surfaces of a graphene sheet are exterior surfaces readily accessible by an electrolyte, and the effective surface area of a practical graphene-based material depends strongly on its layers of graphene nanosheets.5,6 To date, a great deal of effort has been devoted to exploring graphene-based electric double-layer capacitors (EDLCs).5 16 For example, graphene sheets prepared by chemical vapor deposition can be used to fabricate ultrathin layer EDLCs with high rate capability.14 On the other hand, chemically converted graphene (CCG) materials can be prepared in large scale and at low costs.1,2 Furthermore, EDLCs based on CCG sheets with aqueous electrolytes exhibited high specific capacitances of 135 to 205 F g 1,7,8 which are comparable to or higher than those of the EDLCs based on active carbon or carbon nanotubes.2,17 EDLCs fabricated from curved or surface-modified graphene sheets and using ionic liquids as electrolytes showed ultrahigh energy densities of 65 85 Wh kg 1 because of their high operating voltages.18,19 However, in most of these studies, the high specific capacitances and energy densities were only achievable by charging/discharging at low current densities (
