Chemical bonding of flexible graphene to carbon paper: A new synthetic paradigm for freestanding electrode with high capacitive deionization performance

Capacitive deionization (CDI) has become a promising desalination and water treatment technology due to its low-cost, environment-friendliness and energy-efficient. In this work, it is successful to achieve the preparation of high-quality three-dimensional flexible graphene frameworks (3DFGFs) from commercial carbon paper (CP) by simply combining the modified Hummer's method with freezing drying technology. The electroactive area, conductivity and hydrophilicity are greatly improved, the areal specific capacitance of 3DFGFs electrode reaches 1.43 F/cm(2) at 10 mV/s in 1 M NaCl solution, and the areal adsorption capacity is up to 322.21 (50 mg/L NaCl) and 581.51 mg/m(2) (500 mg/L NaCl), respectively. Interestingly, the overall shape of the 3DFGFs electrode remain intact after 500 times of crimping (capacity retention rate is 96.85% for >500 crimping), suggesting that 3DFGFs have outstanding flexibility owing to the strong interaction between the fibers and the graphene sheets in the frameworks. Finally, we propose a concept of how-to recovery the electrical energy stored in CDI cell. This work opens up a promising direction for the preparation of flexible CDI electrodes, and the simple and mild method developed can be easily applied to the preparation of other flexible electrodes.