Fresh water scarcity is a major threat to sustaining human activities. As noted, approximately 1.1 billion people worldwide lack access to potable water, and a total of 2.7 billion people find water scarce for at least one month of the year.¹ Therefore, efficient, cost-effective, and environmentally friendly desalination technologies need to be developed to secure water accessibility. Capacitive deionization (CDI) is an electrochemical water treatment technology possessing low-pressure operation, minimized maintenance costs, environmental friendliness, and possibly higher energy efficiency than contemporary desalination technologies.²

In literature, diminished salt separation of a CDI unit is often reported during repetitive charging and discharging cycles, along with inversion behavior, i.e., desorption peaks at the beginning of charging (or adsorption) steps, which is primarily accounted for by electrochemical oxidation at the carbon anode (or the positive electrode).3 Such concern recently provoked several studies focusing on how to retain salt separation while mitigating anode oxidation. Successful methods can be summarized as follows: reduction of the charging voltage,4 use of ion-exchange materials,⁵ use of alternating polarization,⁶ operation under inverted CDI (i-CDI) mode,⁷ and modification of the carbon surface.⁸ These efforts have facilitated the development of CDI technology so as to alleviate the threat of water crisis.

In this meeting, we present the use of advanced voltage-based modification to stabilize the capacitive deionization process using predominantly microporous carbon electrodes. The mechanism of the modification on performance improvement will be explained through potential distribution measurements and the modified Donnan (mD) model.

1. https://www.worldwildlife.org/threats/water-scarcity. (Last access: Nov-09-2017)

2. Suss, M. E.; Porada, S.; Sun, X.; Biesheuvel, P. M.; Yoon, J.; Presser, V., Energy Environ. Sci. 2015, 8, 2296-2319

3. Gao, X.; Omosebi, A.; Landon, J.; Liu, K., J. Electrochem. Soc. 2014, 161, E159-E166.

4. Cohen, I.; Avraham, E.; Bouhadana, Y.; Soffer, A.; Aurbach, D., Electrochim. Acta 2013, 106, 91-100.

5. Omosebi, A.; Gao, X.; Landon, J.; Liu, K., ACS Appl. Mater. Interf. 2014, 6, 12640-12649.

6. Gao, X.; Omosebi, A.; Holubowitch, N.; Landon, J.; Liu, K., Electrochim. Acta 2017, 233, 249-255.

7. Gao, X.; Omosebi, A.; Landon, J.; Liu, K., Energy Environ. Sci. 2015, 8, 897-909.

8. Krüner, B.; Srimuk, P.; Fleischmann, S.; Zeiger, M.; Schreiber, A.; Aslan, M.; Quade, A.; Presser, V., Carbon 2017, 117, 46-54