PHOTOELECTROCHEMICAL BEHAVIOR OF NANOCOMPOSITE FILMS OF CADMIUM-SULFIDE, OR TITANIUM-DIOXIDE, AND NICKEL

This paper concerns the photoelectrochemical characterization of nanoc rystalline composite (nanocomposite) films of nickel and CdS (hereafte r designated as Ni/CdS) in aqueous sulfite electrolyte. Experiments we re also conducted on Ni/TiO2 film electrodes in the same electrolyte t o delineate the role of nickel electrochemistry in the photoelectroche mical behavior of the two nanocomposite electrodes. Systematic enhance ment of the photocurrent was observed for Ni/CdS on repeated potential cycling in the sulfite electrolyte. Similar behavior was also seen fo r Ni/TiO2, but the enhancement effect was much smaller. The enhancemen t effect arises from incipient corrosion and subsequent passivation of the nickel matrix, as shown by voltammetry on nickel electrodes in th e sulfite medium. The variant behavior seen for Ni/CdS and Ni/TiO, in turn is attributable to the different degrees of electrochemical stabi lity of nickel in the two composites. The passivation layer on nickel is shown to be Ni(OH)(2) by x-ray photoelectron spectroscopy. Other as pects of the data presented include steeper onset near the bandgap cut off wavelength in the photoaction spectrum for Ni/CdS (relative to the anodically prepared CdS thin film counterpart), lower background curr ents in the dark for Ni/TiO2 (relative to nickel),and stabilization of the nickel matrix against corrosion (in the dark) by the occluded TiO 2 particles.