In order to examine the reliability of carbon xerogel (CX) materials for capacitive deionization (CDI), long-term operation of a CDI cell with CX electrodes was performed in a dilute NaCl solution. During operation at 1.2/0 V, the deionization performance gradually degraded, and a growing inversion peak formed at the beginning of each adsorption step. When the polarity of the electrode was reversed, the use of -1.2/0 V significantly boosted deionization performance. However, this enhancement was not sustained with continued cycling. In this study, we also reported the use of a four-electrode cell, in which the potential distribution for a pair of electrodes could be measured, and the potential of zero charge (PZC) for a single electrode could be located. Based upon the PZC location for the used electrodes with respect to the corresponding potential distribution, performance variation and the formation of the inversion peak for long-term CDI operation were interpreted. In addition, N-2 adsorption-desorption measurements and surface morphology examinations indicated that there was little variation in the porosity of the cycled electrodes with long-term operation. (C) 2014 The Electrochemical Society. All rights reserved.