Optimal Ag concentration for H₂ production via Ag:TiO ₂ nanocomposite thin film photoanode

TiO₂ thin films containing different concentrations of Ag nanoparticles have been synthesized by sol-gel method. According to UV-visible spectra, presence of an intense surface plasmon resonance peak at 490 nm of wavelength indicated formation of silver nanoparticles in the TiO₂ films. Based on atomic force microscopy (AFM) analysis, the surface roughness and the effective surface ratio increased by increasing the Ag mol%. Moreover, scanning electron microscopy (SEM) images showed formation of Ag nanoparticles on the surface for the samples containing high Ag concentration. X-ray diffraction (XRD) patterns revealed that the size of Ag nanocrystals increased by increasing the Ag content in the films while the nanocrystalline size of TiO₂ reduced in the presence of silver nanoparticles. Based on x-ray photoelectron spectroscopy (XPS) data, a stoichiometric chemical composition was detected for TiO₂ while, Ag presented in a combination a metal/oxide states on the surface. Studying photoresponse of the samples showed that the highest photocurrent was obtained for the sample containing 1 mol% Ag. By measuring the photovoltage versus time, it was found that addition of silver nanoparticles to the TiO₂ layer resulted in reduction of the transient time of the photogenerated carriers in the samples. Impedance spectroscopy determined a slight decrease in charge transfer resistance by addition of Ag to the films. Moreover, measuring the amount of hydrogen produced during water splitting reactions verified that the highest quantum yield of 9.6% was obtained for the sample with 1 mol% Ag.