TY - JOUR

T1 - Current-Induced Membrane Discharge

A1 - Andersen,Mathias Bækbo

A1 - van Soestbergen,M.

A1 - Mani,A.

A1 - Bruus,Henrik

A1 - Biesheuvel,P. M.

A1 - Bazant,M. Z.

AU - Andersen,Mathias Bækbo

AU - van Soestbergen,M.

AU - Mani,A.

AU - Bruus,Henrik

AU - Biesheuvel,P. M.

AU - Bazant,M. Z.

PB - American Physical Society

PY - 2012

Y1 - 2012

N2 - Possible mechanisms for overlimiting current (OLC) through aqueous ion-exchange membranes (exceeding diffusion limitation) have been debated for half a century. Flows consistent with electro-osmotic instability have recently been observed in microfluidic experiments, but the existing theory neglects chemical effects and remains to be quantitatively tested. Here, we show that charge regulation and water self-ionization can lead to OLC by "current-induced membrane discharge'' (CIMD), even in the absence of fluid flow, in ion-exchange membranes much thicker than the local Debye screening length. Salt depletion leads to a large electric field resulting in a local pH shift within the membrane with the effect that the membrane discharges and loses its ion selectivity. Since salt co-ions, H+ ions, and OH- ions contribute to OLC, CIMD interferes with electrodialysis (salt counterion removal) but could be exploited for current-assisted ion exchange and pH control. CIMD also suppresses the extended space charge that leads to electroosmotic instability, so it should be reconsidered in both models and experiments on OLC.

AB - Possible mechanisms for overlimiting current (OLC) through aqueous ion-exchange membranes (exceeding diffusion limitation) have been debated for half a century. Flows consistent with electro-osmotic instability have recently been observed in microfluidic experiments, but the existing theory neglects chemical effects and remains to be quantitatively tested. Here, we show that charge regulation and water self-ionization can lead to OLC by "current-induced membrane discharge'' (CIMD), even in the absence of fluid flow, in ion-exchange membranes much thicker than the local Debye screening length. Salt depletion leads to a large electric field resulting in a local pH shift within the membrane with the effect that the membrane discharges and loses its ion selectivity. Since salt co-ions, H+ ions, and OH- ions contribute to OLC, CIMD interferes with electrodialysis (salt counterion removal) but could be exploited for current-assisted ion exchange and pH control. CIMD also suppresses the extended space charge that leads to electroosmotic instability, so it should be reconsidered in both models and experiments on OLC.

UR - http://prl.aps.org/abstract/PRL/v109/i10/e108301

U2 - 10.1103/PhysRevLett.109.108301

DO - 10.1103/PhysRevLett.109.108301

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 10

VL - 109

SP - Paper 108301

ER -