Electron transport in silver-semiconductor nanocomposite films exhibiting multicolor photochromism

Abstract

In the multicolor photochromism of TiO₂ nanoporous films loaded with photocatalytically deposited Ag nanoparticles, visible light-induced electron transfer from Ag to oxygen molecules plays an essential role. Here we examined the effect of TiO₂ on the electron transfer. We found that not only photocatalytically deposited Ag, but also electrodeposited Ag and commercially available Ag nanoparticles in a nanoporous TiO₂ film exhibit the multicolor photochromism. The electrodeposited Ag exhibits the multicolor photochromism also in a nanoporous ZnO film, but not in nanoporouns indium–tin oxide (ITO) and SiO₂ matrices. Photoelectrochemical measurements for the Ag-TiO₂ nanocomposite elucidated that some of the photo-excited electrons on Ag are transferred to oxygen molecules via TiO₂ and non-excited Ag. Thus, an n-type semiconductor plays an important role in the charge separation between the excited electrons and Ag⁺. Non-excited Ag on TiO₂ also plays an important role in the charge separation and/or catalysis of oxygen reduction. Replacement of the non-excited Ag with Pt accelerated the electron transport from the photo-excited Ag to oxygen molecules and the photochromic behavior.