Cation Extraction Process in Bilayer Cyanide Film as Investigated by Depth-Resolved X-ray Absorption Spectroscopy

The cation extraction process in the bilayer cyanide film with an epitaxial interface, Na0.84-y Co2+[Fe y 3+Fe1-y 2+(CN)6]0.713.8H2O (NCF71)/Na1.60-x (Co x 3+Co1-x 2+)[Fe2+(CN)6]0.902.8H2O (NCF90), was investigated by depth-resolved X-ray absorption spectroscopy. Assuming stepwise depth (z) distributions of Co3+ and Fe3+, we estimated the step depths, d Co and d Fe, and concentrations, δCo and δFe, of the respective ions against the average quantity (δav) of cation extraction. The Na+ extraction was found to be dominant in the NCF90 surface layer, consistent with the lower redox potential in the NCF90 layer. We found that the magnitude of d Fe (∼600 nm) is much deeper than the actual depth (d = 200 nm) of the NCF71/NCF90 interface, and interpreted the behavior in terms of the redox interaction in the vicinity of the interface.