Elucidation of the electrochromic mechanism of nanostructured iron oxides films

Nanostructured hematite thin films were electrochemically cycled in an aqueous solution of LiOH. Through optical, structural, morphological, and magnetic measurements, the coloration mechanism of electrochromic iron oxide thin films was elucidated. The conditions for double or single electrochromic behavior are given in this work. During the electrochemical cycling, it was found that topotactic transformations of hexagonal crystal structures are favored; i.e. α-Fe2O3 to Fe(OH)2 and subsequently to δ-FeOOH. These topotactic redox reactions are responsible for color changes of iron oxide films.