Surface Morphology/Composition and Photoelectrochemical Behavior of Metal−Semiconductor Composite Films

Scanning electron microscopy was used to study the morphology of metal−TiO 2 composite films prepared for photoelectrochemical applications. These films consisted of electrodeposited Ni, Cu, Ag, or In with TiO 2 (Degussa P-25) particles occluded in them. In the case of Ni−TiO 2 composites, co-clusters of nickel and TiO 2 were observed superimposed on the “flat” regions of the film containing only nickel. This co-cluster formation facilitated efficient separation of photogenerated electron−hole pairs in the TiO 2 component. On the other hand, the distribution of TiO 2 on the indium film surface was such that electron−hole pair recombination resulted on photoexcitation of TiO 2 . Whereas Cu−TiO 2 composite films exhibited n-type photoelectrochemical behavior in pH 7 sulfite medium, p-type activity resulted when the photovoltammetry experiment was repeated in 0.1 M NaOH. This behavior was attributed to Cu 2 O formed in situ in the Cu−TiO 2 composite film.