Flexible energy storage devices have received great interest in many emerging wearable or rolling-up modern gadgets, such as electronic papers, collapsible displays and other personal multimedia devices.[1, 2] These applications not only require electrode materials with good electrochemical properties, but also with high mechanical integrity upon bending or folding, compact design and lightweight property.[3, 4] Among various types of energy storage devices, supercapacitors have attracted significant attention due to its ability to balance the need of high energy density of battery and fast power delivery of capacitor.[5] However, most of the conventional supercapacitor devices that are currently available in the market are based on rigid electrodes, thus they are not suitable to be used in the flexible energy storage devices.[2, 5] Recent literature has introduced free-standing carbon-based papers which are promising for producing flexible supercapacitor devices.[2–4, 6] Carbon nanotubes (CNT) and its composites have been widely studied to form flexible electrodes.[7, 8] However, their relatively high production cost and difficulty of achieving stable CNT dispersion have hindered their practical application.[4] Recently, graphene-based electrodes have gained interest due to their remarkable mechanical and electrical properties as well as good electrochemical stability.[3, 4, 9, 10] A graphene-based symmetric supercapacitor device has been reported with capacitance of 205 F g− 1. In this study, graphene and binder were mixed and deposited onto Ni foam current collector.[11] In order to form free-standing and flexible electrodes, assembly of individual graphene nanosheets into a macroscopic graphene-based paper is of particular interest. Several recent reports on free-standing graphene papers have shown remarkable flexibility upon bending and high gravimetric capacitance (F g− 1). However, the mass of their electrodes are generally very low (< 0.5 mg cm− 2), resulting in the low capacitance per area (mF cm− 2). Graphene cellulose paper has been reported with areal capacitance of 81 mF cm− 2 (120 F g− 1).[2] Carbon black has been introduced as spacers within graphene sheets in flexible graphene paper, achieving areal capacitance of 56.6 mF cm− 2