Abstract: The ion selectivity of nickel hexacyanoferrate thin film to alkali cations in ESIX (electrochemically switched ion exchange) processes was investigated using molecular dynamics(MD) techniques; water and cation (Na⁺ and Cs⁺) intercalation, configuration, and dynamics in reduced nickel hexacyanoferrate structures with different cation combinations were studied and compared with the experimental results. In the simulations, water was represented by an extended simple point-charge(SPC/E) model, and all other atomic interactions were represented by a universal force field(UFF). The potential energies of various cations combination (Cs⁺ and Na⁺) in reduced i-NiHCF and 1 mol/L Cs/NaCl mixed solution were obtained. In most cases, the total potential energy of the solid is reduced when water is intercalated into the various reduced NiHCF structures. Combining the solid and the solution simulation results, it is shown that the solid composition of 3Cs⁺/1Na⁺ is the stablest structure form (NaCs₃Ni₄[Fe(CN)₆]₃) over a range of solution compositions.

Key words: nickel hexacyanoferrate; molecular dynamics simulation; ion selectivity; thin film; electrochemically switched ion exchange