Bilayer electrodes of TiO2-GO: influence of the interfacial properties on the electroreduction of graphene oxide

The combination of titanium oxide (TiO2) and graphene provides an opportunity to develop novel functional materials for many applications. Recent reports on the electrochemical reduction of colloidal solutions of graphene oxide onto TiO2 have opened the route for interesting electrode architectures. To optimize these electrodes, it is important to understand the role of the electronic and chemical properties of TiO2 in the conversion of graphene oxide (GO) into graphene. In this work, we study the effect of the interfacial properties of the bilayer system on the electrochemical reduction of GO. Anodized titanium oxide with dissimilar surface properties was obtained by varying the composition of the anodizing bath and by controlling the crystallinity through thermal treatments. Differences on the yield and nature of oxygenated functional groups and graphene domains after electrochemical reduction suggest that surface chemistry and crystallinity of the oxide determine the bonding with GO and that this is favored through the epoxide and hydroxyl groups in nearly stoichiometric and crystalline TiO2 surfaces, whereas hydroxyl groups are dominant in oxide films with abundance of amorphous phase. The synthesis of TiO2 using sulfuric acid promotes higher oxide crystallinity that facilitates the reduction of oxygenated groups in GO, whereas phosphoric acid seems better suited for inducing the formation of graphene domains, indicating the removal of oxygen functionalities attached to GO basal plane. These findings are relevant to the tailoring of bilayer electrodes of TiO2-GO for energy and environmental applications.