One-step anodization-electrophoretic deposition of titanium nanotubes-graphene nanoribbon framework for water oxidation

Abstract

Self-supported titanium nanotubes (TNT) is one of the most interesting materials for environmental applications. However, its major hurdle is the low absorption throughout the visible range; therefore, high rate of exciton separation is hardly archived. We introduce a new strategy to incorporate a graphene nanoribbon framework (GNF-1), a subclass of porous organic polymer, onto TNT by means of a one-step anodization-electrophoretic deposition assisted by the anionic surfactant sodium dodecyl sulfate. This approach leads to the formation of an effective interface between the TNT and GNF-1 based on the simultaneous anodic growth of nanotubular TiO2 and the electrophoretic-driven motion of the negatively charged GNF-1-surfactant colloids. The use of an anionic surfactant is mandatory to attract the charge neutral GNF-1 to the anode and can be easily expanded to other porous organic polymers. The TNT-GNF-1 electrode exhibits enhanced performance as a photoanode, with an increase in photocurrent density up to 45% relative to pristine TNT electrode. This result is related to the higher charge separation and the slightly valence band maximum shift, which is beneficial for transfer of charge carriers for water oxidation. The faradaic efficiency of both the pristine TNT and TNT-GNF-1 photoanodes to generate O2 is 70% according to a collector-generator dual electrode system, demonstrating that the increase in photocurrent response of TNT-GNF-1 photoanodes is not due to oxidation of GNF-1, but from the synergic effect between the materials.