Abstract
Photoelectrochemical responses and unique current switching behavior of silver nanoparticles (Ag NPs) coated with TiO2 are presented. Cathodic photocurrent response is obtained near the open circuit potential (OCP) of this Ag NP modified TiO2 electrode under visible light (> 420 nm), and the current can be switched to anodic photocurrent under ultra-violet (UV) light illumination. Such interesting photocurrent switching characteristic can be observed only when Ag NPs are embedded under TiO2 film, but not in bare Ag NP, TiO2, Ag NP-coated TiO2 electrode, or Ag oxide electrode. The switching behavior can be explained by direct electron transfer from Ag NPs to TiO2 under visible light with dissolved oxygen as electron acceptor, and opposite current flow when TiO2 is excited by UV light. Photocurrent response to excitation wavelength and effects of Ag NP density are studied. Photoelectrochemical response in visible range resembles the extinction spectrum of Ag NPs. Photocurrent and spectrum broadening increase with Ag NP particle density, indicating strong dependence of the PEC switching behavior on collective responses of Ag surface plasmons by interacting with each other.
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