Enhanced photo-electrochemical performance of reduced graphene-oxide wrapped TiO<inf>2</inf> multi-leg nanotubes

We report the synthesis and photo-electrochemical properties of reduced graphene oxide wrapped multi-leg TiO2 nanotubes (MLNTs). The TiO2 nanotubes fabricated by electrochemical anodization were subsequently wrapped with graphene oxide (GO)/ reduced graphene oxide (rGO) using silanization method. Use of separated (multi-leg/branched) TiO2 nanotubes and suitable optimization of the silanization parameters helped to achieve near-conformal wrapping of the nanotubes by GO/rGO layers. The photo-electrochemical performance of rGO/TiO2 samples with multi-leg morphology were studied in 0.5 M Na2SO4 aqueous solution under the illumination of simulated sunlight (AM 1.5G, 100 mW/cm2) and was compared with rGO modified regular (compact) TiO2 nanotubes under similar conditions. Substantial improvement in "applied bias photon to current conversion efficiency" (% ABPE) was observed for rGO wrapped TiO2 multi-leg nanotubes over that of nanotubes without wrapping. Diffuse reflectance spectroscopy was performed to investigate the light scattering capability of the nanotubes arrays, which revealed higher scattering and hence better light harvesting ability of MLNT's. The electrochemical impedance spectroscopy was used to study the charge transfer characteristics across rGO/TiO2 interface. The results showed a decrease in charge transfer resistance for rGO wrapped TiO2 multi-leg nanotubes which helped in the enhancement of photo-electrochemical performance.