Perfect divalent cation selectivity with capacitive deionization

Rana Uwayid, Eric N. Guyes, Amit N. Shocron, Jack Gilron, Menachem Elimelech, Matthew E. Suss

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


Capacitive deionization (CDI) is an emerging membraneless water desalination technology based on storing ions in charged electrodes by electrosorption. Due to unique selectivity mechanisms, CDI has been investigated towards ion-selective separations such as water softening, nutrient recovery, and production of irrigation water. Especially promising is the use of activated microporous carbon electrodes due to their low cost and wide availability at commercial scales. We show here, both theoretically and experimentally, that sulfonated activated carbon electrodes enable the first demonstration of perfect divalent cation selectivity in CDI, where we define “perfect” as significant removal of the divalent cation with zero removal of the competing monovalent cation. For example, for a feedwater of 15 mM NaCl and 3 mM CaCl2, and charging from 0.4 V to 1.2 V, we show our cell can remove 127 μmol per gram carbon of divalent Ca2+, while slightly expelling competing monovalent Na+ (-13.2 μmol/g). This separation can be achieved with excellent efficiency, as we show both theoretically and experimentally a calcium charge efficiency above unity, and an experimental energy consumption of less than 0.1 kWh/m3. We further demonstrate a low-infrastructure technique to measure cation selectivity, using ion-selective electrodes and the extended Onsager-Fuoss model.

Original languageEnglish
Article number117959
JournalWater Research
StatePublished - 15 Feb 2022


  • Activated carbon
  • Capacitive deionization
  • Desalination
  • Divalent selectivity
  • Sulfonated cathode
  • Water softening
  • ion selective separations

ASJC Scopus subject areas

  • Water Science and Technology
  • Ecological Modeling
  • Pollution
  • Waste Management and Disposal
  • Environmental Engineering
  • Civil and Structural Engineering


Dive into the research topics of 'Perfect divalent cation selectivity with capacitive deionization'. Together they form a unique fingerprint.

Cite this