The role of surface chemistry in the charge storage properties of graphene oxide

In the present study we have evaluated the contribution of particular oxygen functional groups in the charge storage properties of graphene oxide (GO). This was achieved by a gradual thermal reduction of GO in an inert atmosphere (up to 800 degrees C) and thorough examination of functional groups which remained after each de-functionalization step. After identification of functional groups, the character of additional cyclovoltammetric peak, less pronounced than the main redox quinone/hydroquinone pair, and overall charge storage properties of GO were discussed from the perspective of different thermal stability of its surface groups. The results indicated three-stage deoxidation process of GO, each comprising of specific surface chemistry, structural changes and electrochemical behavior. The low capacitance, similar to 50 F g(-1), at T <= 300 degrees C was attributed to the presence of epoxy and carboxyl groups. The highest capacitance (120-130 F g(-1)) was observed in the case of GO reduced at 400 and 500 degrees C, which we attributed to positive effects of phenol and carbonyl/quinone groups, while at high temperatures (T >= 600 degrees C, similar to 30 F g(-1)) the extensive desorption of functional groups and structural changes were emphasized as the main reasons for additional decrease of capacitance. Our results highlight the cases where the duality of interpretation of surface functional groups is likely to happen and indicate that not all functional groups play a positive role in charge storage behavior of graphene oxide. (C) 2017 Elsevier Ltd. All rights reserved.