Charge storage in nanotubes: the case of a 2-1 electrolyte

TL;DR

This paper investigates charge storage mechanisms in narrow nanotubes with a 2-1 electrolyte, revealing how ion valence and tube ionophilicity influence filling behavior and electrochemical potential.

Contribution

It introduces a novel analysis of ion filling in nanotubes with asymmetric electrolytes, emphasizing the role of electrochemical potential and screening effects.

Findings

Ionophobic tubes are filled with dilute gas of ions.

Ionophilic tubes contain a one-dimensional solid of ions.

Filling patterns depend on the applied electrode potential and ion interactions.

Abstract

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.