Photoelectrochromism in Chemically Modified Nickel−Titanium Dioxide Nanocomposite Films

A new approach to photoelectrochromism based on chemical modification of a nickel−TiO2 nanocomposite film is described. Such nanocomposite films, previously developed in our laboratory, are comprised of TiO2 particles that are dispersed in a continuous nickel matrix. Either chemical or electrochemical modification of the nickel component in a ferricyanide medium results in a surface layer of nickel hexacyanoferrate (NHF). Photoexcitation of TiO2 results in electron transfer to NHF and a photoelectrochromic transition of the film from yellow to blue. The reverse transition can be electrochemically driven in the dark.