  Using porous electrodes containing nickel hexacyanoferrate (NiHCF)
nanoparticles, we construct and test a device for capacitive deionization in a
two flow-channel device where the intercalation electrodes are in direct
contact with an anion-exchange membrane. Upon negatively charging NiHCF,
cations intercalate into it and the water in its vicinity is desalinated; at
the same time water in the opposing electrode becomes more saline upon
positively charging the NiHCF in that electrode. In a cyclic process of charge
and discharge, fresh water is continuously produced, alternating between the
two channels in sync with the direction of applied current. We present
proof-of-principle experiments of this technology for single salt solutions,
where we analyze various levels of current and cycle durations. We analyze salt
removal rate and energy consumption. In desalination experiments with salt
mixtures we find a threefold enhancement for K$^+$ over Na$^+$-adsorption,
which shows the potential of NiHCF intercalation electrodes for selective ion
separation from mixed ionic solutions.
