  We consider a 2-1 electrolyte in contact with a narrow nanotube, which only
allows one-dimensional storage along the axis. The asymmetry does not allow an
a priori definition of the potential of zero charge; instead, the natural
reference is the electrode potential at which both ions have the same
electrochemical potential; the value of the latter can serve as a measure of
ionophilicity. Near this potential, ionophobic tubes are filled with a dilute
gas, ionophilic tubes are filled with a one-dimensional solid containing about
the same number of the divalent ions and the monovalent counterions, a
structure that is stabilized by a strong screening of the Coulomb interaction
by an induced counter charge on the walls of the tube. The filling of the tube
by the application of an electrode potential exhibits a complicated pattern of
interactions between the two kinds of ions.
