An Ellipsometric Investigation of the Formation and Conversion of Prussian Blue Films

Ellipsometry has been used to study the formation and electrochromic conversion of Prussian blue films. A Prussian blue film can be deposited on a metal substrate in an appropriate electrolyte by applying a cathodic current. Once grown, a given film can be cycled from its original blue color to a transparent state by applying a cathodic current. The film can also be cycled back to a blue color again with an anodic current; however, the blue film after the first and subsequent cycles has optical properties that differ from the original blue film. At potentials higher than that which return the film to its blue color, the film changes once more, but if the potential is allowed to become too high, the film changes in an irreversible manner.