Binder-free 3D graphene nanostructures on Ni foam substrate for application in capacitive deionization

Hereby a simple, low-cost and scalable route is being presented for preparation of binder-free electrodes of reduced graphene oxide (RGO) on Ni foam (Ni/Gr). In this regard, the Ni foams are dipped in graphene oxide (GO) slurry. Next, the GO loaded Ni foams are kept in a freeze dryer for 24 h and heated up to 800 °C in an inert atmosphere. In this approach, the amount of active materials can be easily optimized for capacitive deionization (CDI). The characterization of Ni/Gr electrodes revealed a 3D porous assembly of RGO on Ni substrate which is helpful for the fast ion diffusion and rapid electron transport. The electrochemical performance of the prepared electrodes is investigated in both 3-electrode system and symmetric 2-electrode assembly. Then, the prepared electrodes are applied for capacitive deionization (CDI) studies in saline water samples. Results revealed a specific capacitance of about 77 F/g (in 1 M of NaCl at 2.5 A/g) and an ion removal capacitance of 22.3 mg/g (in 50 mL of 500 ppm of NaCl) for the fabricated system. The stability of the CDI system was surveyed in 500 ppm of NaCl solution which showed 65% of the initial capacity after 200 consecutive cycles (9 days). These results indicate that this method is efficient for both supercapacitive energy storage applications and CDI technology.