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Issue 5, 2021

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

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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.

Graphical abstract: Emerging investigator series: local pH effects on carbon oxidation in capacitive deionization architectures

Supplementary files

Article information


Submitted
03 Jan 2021
Accepted
17 Mar 2021
First published
19 Mar 2021

Environ. Sci.: Water Res. Technol., 2021,7, 861-869
Article type
Paper

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

J. Landon, X. Gao, A. Omosebi and K. Liu, Environ. Sci.: Water Res. Technol., 2021, 7, 861 DOI: 10.1039/D1EW00005E

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