New testing procedures of a capacitive deionization reactor

Abstract

Currently, according to conventional charge-discharge profiles, energy consumed in charging Capacitive Deionization (CDI) systems is always a function of different parameters (current used for charging, capacitance and current employed for discharging) making it difficult to separate the effect of these parameters on CDI performance and energy efficiency. Thus, energy efficiencies are strongly influenced by the current in the preceding charge or discharge stage of the process. We find consistently that this phenomenon, which to our knowledge has not been addressed in previous CDI communications, is much more intense when different currents are applied for each of the charging and discharging cycles. The investigation reported here provides a mechanistic analysis of the operational aspects of CDI and develops a new procedure that allows for a precise evaluation of performance and energy efficiency. Furthermore, the model developed here allows one to separate charge and discharge cycles, and therefore contributes to the possibility of defining an operational mode for real-world devices in which effective separation of deionization and regeneration steps needs to be implemented. This method of analysis could be useful not only for CDI but also for other electrochemical systems such as in secondary batteries and supercapacitors where charge and discharge are typically employed.

Evaluation of operational parameters for a capacitive deionization reactor employing asymmetric electrodes

“…These amounts were generally lower than that found by Huyskens et al [39] (70%) for MgSO 4. This could be partially explained by the higher solution concentration (more than three times) used in those experiments, which has been previously reported to lead to higher charge efficiencies [40,41]. These losses in charge efficiency may be influenced by the cell potential, backward diffusion of ions and mass transfer limitations [41].…”

Energy consumption analysis of constant voltage and constant current operations in capacitive deionization

“…Energy consumption is a crucial factor when comparing CDI to state of the art desalination technology, reverse osmosis (RO). [3,4] A CDI cell can be operated at various charging modes including constant voltage (CV) [5][6][7][8] and constant current (CC) [7,[9][10][11][12][13][14][15]. Different modes lead to discrepant energy consumption patterns.…”

Energy Consumption and Recovery in Capacitive Deionization Using Nanoporous Activated Carbon Electrodes

“…An important feature of CDI is that part of the energy consumed during charging can be recovered during discharging, a process similar to charge/discharge in electric capacitors. 6,8 CDI could become more cost competitive compared with well-established desalination processes, such as RO, if energy can be recovered in a more efficient way. 1 Energy consumption by CDI is affected by electrosorption and ion transport in well-defined electrode materials.…”

“…1 Due to its simplicity and reliability, capacitive deionization (CDI) has attracted a growing interest for water desalination. [1][2][3][4][5][6][7] Capacitive deionization utilizes highly porous electrodes to remove charged ions in water by electrosorption ( Figure 1). During charging, an electric voltage is applied and ions are driven to oppositely charged electrodes by electrostatic force and entrapped at the electrode-water interface by the formation of an electric double layer (EDL).…”