Emerging investigator series: Local pH effects on carbon oxidation in capacitive deionization architectures

James Landon, Xin Gao, Ayokunle Omosebi, Kunlei Liu

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

In this work, the effect of pH and potential is examined for the oxidation of carbon cloth electrodes used in capacitive deionization (CDI) processes. The degree of oxidation of the electrode surface, examined using the electrode's potential of zero charge (Epzc) and measured using chronoamperometry and cyclic voltammetry, is found to be strongly correlated to the pH of the solution at the interface. Local pH measurements are examined at anodes and cathodes in full CDI and membrane-assisted capacitive deionization (MCDI) cells at cell voltages ranging from 0.3-1.2 V. The cathode is shown to be basic under charging potentials while the anode is found to be acidic. This local pH is found to be highly transient during charging and discharging in CDI cells while the pH is found to be relatively static in the MCDI cells, maintaining a basic pH at the cathode and an acidic pH at the anode even when the cell is discharged. Ion exchange membranes (IEM) are found to have two functions: (1) limiting co-ion expulsion that results from specific ion adsorption and (2) limiting the effects of parasitic Faradaic reactions on the separation process by stabilizing the local pH thereby mitigating dissolved oxygen reduction at the cathode and lessening carbon oxidation at the anode. Performance comparisons including the salt adsorption capacity and charge efficiency are also compared for these systems.

Original languageEnglish
Pages (from-to)861-869
Number of pages9
JournalEnvironmental Science: Water Research and Technology
Volume7
Issue number5
DOIs
StatePublished - May 2021

Bibliographical note

Publisher Copyright:
© 2021 The Royal Society of Chemistry.

ASJC Scopus subject areas

  • Environmental Engineering
  • Water Science and Technology

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