Quasi-Steady-State Polarization Reveals the Interplay of Capacitive and Faradaic Processes in Capacitive Deionization

Nicolas Holubowitch, Ayokunle Omosebi, Xin Gao, James Landon, Kunlei Liu

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

We employ slow cyclic voltammetry to study the quasi-steady-state capacitive deionization (CDI) of aerated 10 mM NaCl from Vcell=−0.2 to 2 V. The method allows for the deconvolution of capacitive and faradaic processes, which are significant even at low voltage, in conjunction with pH, conductivity, dissolved oxygen (DO), and electrode potential measurements. The pH at three locations and effluent DO data identify asymmetric electrosorption in the cell configured with pristine activated carbon electrodes, where charge is irreversibly consumed to produce H+/OH instead of reversibly adsorbing Cl/Na+. Implementing a reference electrode resolves ion adsorption as a function of the individual potential at each electrode. Near-electrode pH probes reveal pH environments that diverge by up to 8 units during cell polarization and allow more accurate calculation of faradaic redox potentials in a flow-by CDI cell. In the aerated NaCl solution that will be relevant to industrial-scale water treatment, we find that DO reduction occurs to a greater degree than Na+ adsorption at the cathode until DO removal becomes mass transfer limited at <−0.2 V vs. SHE. Two cell architectures – flow-by and flow-through – corroborate our findings. Finally, we reconcile all measurements to generate a map displaying how the potential is partitioned amongst the capacitive and faradaic processes occurring during CDI operation over a 2.2 V window.

Original languageEnglish
Pages (from-to)2404-2413
Number of pages10
JournalChemElectroChem
Volume4
Issue number9
DOIs
StatePublished - Sep 2017

Bibliographical note

Publisher Copyright:
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Keywords

  • capacitive deionization
  • capacitors
  • electrochemical water treatment
  • electrodes
  • oxygen reduction

ASJC Scopus subject areas

  • Catalysis
  • Electrochemistry

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