Design of a highly efficient photoelectrolytic cell for hydrogen generation by water splitting:: Application of TiO2-xCx nanotubes as a photoanode and Pt/TiO2 nanotubes as a cathode

This paper describes the design of a photoelectrochemical (PEC) cell using carbon-doped titanium dioxide (TiO2-xCx) nanotube arrays as the photoanode and platinum, Pt nanoparticles incorporated in TiO2 (titania) nanotube arrays, as the cathode. The PEC cell is found to be highly efficient (i.e., gives good photocurrent at a low external bias, j(p) = 2.5-2.8 mA/cm(2) at -0.4 V-Ag/AgCl), inexpensive (only 0.4 wt % Pt on TiO2), and robust (continuously run for 80 h without affecting the photocurrent) for hydrogen generation by water splitting under the illumination of simulated one sun intensity. The synthesis of the photoanode is carried out by the sonoelectrochemical anodization technique using aqueous ethylene glycol and ammonium fluoride solution. This anodization process gives self-organized hexagonally ordered TiO2 nanotube arrays with a wide range of nanotube structure, which possess good uniformity and conformability. As-synthesized titania nanotubes are annealed under reducing atmosphere (H-2), which converts the amorphous nanotube arrays to photoactive anatase phase as well as it helps in doping of the carbon (from the reduction of ethylene glycol) to give the TiO2-xCx type photoanode. The cathode material is prepared by synthesizing Pt nanoparticles (by reduction of a Pt salt to Pt(0)) into the titania nanotubular arrays by the incipient wetness method. Various characterization techniques, viz., field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, electron diffraction, and glancing angle X-ray diffraction, etc., are used to study the morphology, phase, band gap, and doping of the nanotubes.