Photoelectrochemical behavior of nanocomposite films of cadmium sulfide, or titanium dioxide, and nickel

This paper concerns the photoelectrochemical characterization of nanocrystalline composite (nanocomposite) films of nickel and CdS (hereafter designated as Ni/CdS) in aqueous sulfite electrolyte. Experiments were also conducted on Ni/TiO2 film electrodes in the same electrolyte to delineate the role of nickel electrochemistry in the photoelectrochemical behavior of the two nanocomposite electrodes. Systematic enhancement of the photocurrent was observed for Ni/CdS on repeated potential cycling in the sulfite electrolyte. Similar behavior was also seen for Ni/TiO2, but the enhancement effect was much smaller. The enhancement effect arises from incipient corrosion and subsequent passivation of the nickel matrix, as shown by voltammetry on nickel electrodes in the sulfite medium. The variant behavior seen for Ni/CdS and Ni/TiO, in turn is attributable to the different degrees of electrochemical stability of nickel in the two composites. The passivation layer on nickel is shown to be Ni(OH)(2) by x-ray photoelectron spectroscopy. Other aspects of the data presented include steeper onset near the bandgap cutoff wavelength in the photoaction spectrum for Ni/CdS (relative to the anodically prepared CdS thin film counterpart), lower background currents in the dark for Ni/TiO2 (relative to nickel),and stabilization of the nickel matrix against corrosion (in the dark) by the occluded TiO2 particles.