Overlimiting current and shock electrodialysis in porous media

Daosheng Deng, E. Victoria Dydek, Ji Hyung Han, Sven Schlumpberger, Ali Mani, Boris Zaltzman, Martin Z. Bazant

Research output: Contribution to journalArticlepeer-review

105 Scopus citations

Abstract

Most electrochemical processes, such as electrodialysis, are limited by diffusion, but in porous media, surface conduction and electroosmotic flow also contribute to ionic flux. In this article, we report experimental evidence for surface-driven overlimiting current (faster than diffusion) and deionization shocks (propagating salt removal) in a porous medium. The apparatus consists of a silica glass frit (1 mm thick with a 500 nm mean pore size) in an aqueous electrolyte (CuSO4 or AgNO3) passing ionic current from a reservoir to a cation-selective membrane (Nafion). The current-voltage relation of the whole system is consistent with a proposed theory based on the electroosmotic flow mechanism over a broad range of reservoir salt concentrations (0.1 mM to 1.0 M) after accounting for (Cu) electrode polarization and pH-regulated silica charge. Above the limiting current, deionized water (≈10 μM) can be continuously extracted from the frit, which implies the existence of a stable shock propagating against the flow, bordering a depleted region that extends more than 0.5 mm across the outlet. The results suggest the feasibility of shock electrodialysis as a new approach to water desalination and other electrochemical separations.

Original languageEnglish
Pages (from-to)16167-16177
Number of pages11
JournalLangmuir
Volume29
Issue number52
DOIs
StatePublished - 31 Dec 2013

ASJC Scopus subject areas

  • Materials Science (all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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