Functionalized Graphene/Activated Carbon Composite Electrodes for Asymmetric Capacitive Deionization

Aminated graphene (GP-NH2) was fabricated via the modification of graphite oxide (GO) with 3-aminopropyltriethoxysilane (AMPTS), and the covalent grafting of the amine functional groups was confirmed using Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray (EDX) spectroscopy. The aminated graphene (GP-NH2)/activated carbon (AC) composite electrode (GP-NH2/AC) was prepared, using the GP-NH2 as an additive. An AC parallel to GP-NH2/AC asymmetric capacitor for capacitor deionization was then assembled using the GP-NH2/AC electrode as the positive electrode and AC as the negative electrode. A salt removal of 7.63 mg.g(-1) was achieved using the AC parallel to GP-NH2/AC capacitor, and current efficiency was increased to 77.6%. AGP-SO3H/AC electrode was then prepared by mixing AC with sulfonated GP. With GP-NH2/AC as the positive electrode, and GP-SO3H/AC as the negative electrode, a GP-SO3H/AC parallel to GP-NH2/AC asymmetric capacitor was assembled for capacitive deionization. An average desalting rate of 0.99 mg.g(-1).min(-1) was achieved, almost five times higher than that achieved using an AC parallel to AC symmetric capacitor. The charge-discharge rate showed a 30% increase. The existence of the intrinsic charge on the electrode surface greatly inhibited the migration of counter ions, so that the current efficiency was significantly enhanced (to 92.8%) in comparison with the value achieved using an AC parallel to AC capacitor (40%). These results demonstrated that the functionalized graphene in the AC electrode not only enhanced the conductivity, but also controlled the selective adsorption of ions, thereby significantly improving the deionization performance.