Nanofluidic ion-exchange membranes
Can their conductance compete with polymeric ion-exchange membranes?
Kostadin V. Petrov (TU Delft - ChemE/Transport Phenomena)
J. Hurkmans (TU Delft - Fluid Mechanics)
Remco Hartkamp (TU Delft - Complex Fluid Processing)
D.A. Vermaas (TU Delft - ChemE/Transport Phenomena)
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Abstract
Nanofluidic membranes (NFMs) are gaining prominence as alternative ion-exchange membranes, because of their distinct selectivity mechanism, which does not rely on functional groups on a polymeric backbone but rather on charged nanopores that allow straight ion-conductive pathways for efficient ion transport. We measured the conductivity of commercial anodized aluminum oxide membranes with different pore sizes under different current densities and electrolyte concentrations. We also simulated a nanopore channel with charged walls between two electrolyte reservoirs. Our findings indicate that electrolyte concentration is the main parameter that determines NFM conductivity, with a linear dependence at least up to 1 M. Our study shows that the optimal pore length is between 0.5 and 5 μm considering the trade-off between selectivity and conductance. On the other hand, the conductance is not sensitive to the pore diameter. Conical nanopores are a way to increase conductance, but according to our results, this increase comes at the expense of selectivity. Our findings suggest that NFMs can outperform polymeric ion-exchange membranes in certain electrochemical applications, such as reverse electrodialysis, but not in applications that use low electrolyte concentrations on both sides of the membrane.
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