Actual structure of dissolved zinc ion restricted in less than 1 nanometer micropores of carbon

The structures and properties of hydrated ions confined in solid nanospaces are not substantially understood, although they are indispensable for the development of new devices such as electrical double-layer capacitors. We describe the hydration structure around a Zn²⁺ restricted in slit-shaped micropores of two kinds of activated carbon fibers (ACF) by the analysis of X-ray absorption fine structure (XAFS) spectra. The proportion of dissolved species against the total adsorbed amounts of Zn²⁺on ACF was decreased with the reduction of the average micropore width of ACF. We could trace the actual structure of "nanosolution" around a Zn²⁺ restricted in less than 1 nm pore by extended XAFS (EXAFS) spectra with applying these values. Our results strongly indicate that the dehydrated structure can be stably formed inside the micropore whose pore size is less than the total diameter of the symmetrically hydrated ion, where the dehydrated ions can be stabilized by the strong potential well of the micropore.