Synthesis of Functional Nanostructured TiO2 Photo Active Membranes for Room Temperature Water Splitting

Photo assisted splitting of water at room temperature to produce hydrogen on a liquid-semiconductor (L-S) interface holds great technological importance toward hydrogen economy. In order to electrochemically split water into H₂ and O₂, thermodynamic electrochemical potential (E₀) of 1.23 V (Vs NHE) is required, where E_reduction is at 0 V(Vs NHE) for H₂ half cell reaction (2H⁺ + 2e^- àH₂) and E_oxidation is -1.23 V(Vs NHE) for O₂ half cell reaction (2OH^- à 2H⁺ + 2e^-+ O₂). The above reactions occurs preferentially on a L-S interface under solar radiation. Various semiconductors such as CdS, InP, SiC, Si, TiO₂, Ta₂O₃, Fe₂O₃ and SrTiO₃ have been studied as a potential photo-catalyst for photolysis of water. However, majority of these materials have shown a poor stability to photo oxidative corrosion with TiO₂ being an exception. TiO₂ is a broadband semiconductor with E_g ~ 3.1eV (UV) and a relatively poor electronic conductor. However, its electronic properties can be improved by controlling its shape and chemical composition. This contribution focuses on the synthesis and application of specific TiO₂ based functional nanostructures in a form of a membrane for photo assisted water splitting application. The proposed functional membrane structure has an advantage over the conventional approach i.e. colloidal TiO₂. In the present work, an attempt has been made to take advantage of superior directional electronic transport in TiO₂ nanotubes (nt-TiO₂). Under this approach, an nt-TiO₂/Ti/nt-TiO₂ membrane structure was synthesized using electrochemical anodization in fluorine (F^-) based electrolyte. Further, this nt-TiO₂/Ti/nt-TiO₂ membrane structure was modified by preferential deposition of Pt and RuO₂ co-catalysts on either side of the membrane. The selective placement of Pt and RuO₂ on nt-TiO2/Ti/nt-TiO2 membrane structure could prove to be beneficial to achieve physical separation of H₂ and O₂ in a water photolysis reactor utilizing a single electrode scheme.