Abstract
Room temperature simultaneous doping of reduced graphene oxide films with oxygen, nitrogen and chlorine was performed through anodic polarization in a neutral nitrogen-deaerated KCl electrolyte. The thermodynamic electrochemical windows of water, dissolved nitrogen and chlorine anions were analyzed on the basis of the Pourbaix diagram. Anode polarization demonstrated that the nitrogen, water and chlorine anions can be oxidized at an applied potential of 1.7 V vs. NHE. The oxidative products, i.e. oxygen, nitrate anion and hypochlorous acid, can react with the reduced graphene oxide surface. X-ray photoelectron spectroscopy proved the chlorine-nitrogen co-doping of the treated film, along with an increase of oxygen groups. Surface structure evolution was also confirmed by Raman and Fourier-transform infrared spectroscopies. The anodic doping can be hindered by covering the reduced graphene oxide surface with sulfate anions or forming stable carbon-nitrogen bonds. Incorporation of oxygen, nitrogen and chlorine also helps to enhance the supercapacitance of the doped film. (C) 2012 Elsevier Ltd. All rights reserved.