Ultrafast cation intercalation in nanoporous nickel hexacyanoferrate

Cation intercalation into nanoporous coordination polymers is utilized in, e.g., Li(+)/Na(+) secondary batteries, the decontamination of radioactive (137)Cs(+), and so on. Here, we observed an ultrafast intercalation of Na(+) and Rb(+) within 1500 ms in a thin film of nickel hexacyanoferrate, Na0.68Ni[Fe(CN)6]0.675.0H2O, in aqueous solutions. Quantitative analyses of the intercalation kinetics revealed that the high cation diffusion constant (D ∼ 10(-9) cm(2) s(-1)) is responsible for the intercalation.