Optimal Ag2S nanoparticle incorporated TiO2 nanotube array for visible water splitting
Free-standing TiO2 nanotube array (TNA) films were fabricated via two-step anodization of a titanium sheet. The X-ray diffraction pattern indicated amorphous TNAs were transformed into anatase after annealing the films at 500 °C in air. The surface of TNA was modified by a sequential-chemical bath deposition (S-CBD) method to fabricate Ag2S nanoparticles and forming TNA/Ag2S-n nanostructure, by varying the number of cycles (n). Based on SEM observations, the produced films consisted of vertically ordered tubular structure arrays, each with 125 nm in diameter and 4.1 μm in length containing silver sulphide nanoparticles of ∼12 nm diameter. X-Ray photoelectron spectroscopy (XPS) confirmed the formation of Ag2S nanoparticles on TNA film. Increased optical absorption of the TNA/Ag2S system in visible and near infrared was also verified by diffuse reflectance spectroscopy (DRS). Maximum photocurrent density of about 840 μA cm−2 was measured for the synthesized TNA/Ag2S-4 photoanode under visible irradiation which exhibited about 15 fold photo-enhancement in current density as compared with the pure TNAs under similar conditions. The incident photon to current efficiency (IPCE) measurements indicated that the visible response of the samples reached its maximum value of about 20% at a wavelength of 600 nm for the TNA/Ag2S photoanode.