matiori of sodium-containing structures: Na2Co[Fe"(CN)6] or NaCo5[Fe"(CN)6], the more positive peaks at Ca. 0.8 V should be, in our opinion, attributed to the redox behavior of a novel, mixed (e.g., NaKC0Β°FeΒ°(CN)6 or more complex) phase containing both sodium and potassium. We have found from elemental analysis (EDX) that the film contained not only sodium but potassium countercations as well. But color of this reduced C0HCNFe film was green, as expected for a sodium containing CoHCNFe. These results imply that the color of a CoHCNFe film is mainly determined by the nature of countercations which are sorbed into the system from the supporting electrolyte during reduction (Eq. 1). The 'contaminating," cations, which enter and remain in CoHCNFe film due to the history of its use or preparation, seem to have no effect on the system's electrochromic characteristics.
Acknowledgment
We acknowledge support from University of Warsaw (under Grant BW-1301/1/95) and MPI, Italy. P.J.K. appreciates a travel grant from University of Camerino. M.A.M. acknowledges a fellowship from Foundation for Polish Science. We thank K. Filipczuk, University of Warsaw, for technical help.