Ambipolar ion pumping with ratchet-driven active membranes

Alon Herman, Gideon Segev

Research output: Contribution to journalArticlepeer-review

Abstract

In recent years there has been significant progress in the development of artificial ion-pumping membranes. Ion pumps based on asymmetric nanopores have been shown to operate as ionic current rectifiers, thus pumping a net ion flux against a concentration gradient even when driven with unbiased ac signals. However, since ion transport relies on charged nanopores, it is selective to either cations or anions, and thus cannot pump both cations and anions simultaneously. In this paper, we present a model for an electronically active membrane which is based on a flashing ratchet mechanism. The model includes adjacent electrolyte reservoirs and ion-ion interactions, which were not accounted for in prior similar models, and thus provides a better understanding of the driving mechanism and potential capabilities and limitations. It is shown that, unlike most other proposed ion pumps, the ratchet-based ion pump (RBIP) drives both cations and anions in the same direction and up a concentration gradient. This process, referred to as ambipolar ion pumping, is shown to be highly robust for many electrolyte compositions and input signals. The membrane is composed of alternating conductive thin layers (electrodes), separated by insulating layers in an asymmetric design. With insulating layer thicknesses of 70 and 30 nm and an input signal amplitude of 0.5 V, the device drives a salt flux of 0.03 mol/(m2 s) in a mildly saline solution (10 mM). Thus, RBIPs may pave the way for many exciting future applications involving ambipolar ion pumping, most notably for desalination.

Original languageEnglish
Article number034056
JournalPhysical Review Applied
Volume21
Issue number3
DOIs
StatePublished - Mar 2024

Funding

FundersFunder number
European Commission
Azrieli Foundation
European Research Executive Agency
European Research Council
ESIP-RM101039804

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