Energy Efficiency of Capacitive Deionization

Abstract

Capacitive deionization (CDI) as a class of electrochemical desalination has attracted fast-growing research interest in recent years. A significant part of this growing interest is arguably attributable to the premise that CDI is energy efficient and has the potential to outcompete other conventional desalination technologies. In this review, systematic evaluation of literature data reveals that while the absolute energy consumption of CDI is in general low, most existing CDI systems achieve limited energy efficiency from a thermodynamic perspective. We also analyze the causes for the relatively low energy efficiency and discuss factors that may lead to enhanced energy efficiency for CDI.

The relative insignificance of advanced materials in enhancing the energy efficiency of desalination technologies

“…The thermodynamic energy efficiency, in contrast, is a metric which is appropriate for any desalination method, allowing for the performance of CDI to be placed in context with other technologies. 100,101 Nonetheless, very few studies have reported the thermodynamic energy efficiency of CDI, thus propagating the notion that CDI, with improved electrode materials, can become an energy efficient desalination technology.…”

“…During the charging step of CDI, irreversible energy losses from parasitic side reactions, ion transport resistances (in the spacer channel and electrodes), and electronic resistances (electrode matrix, membranes, current collector, contacts) are inevitable, allowing for only a fraction of the supplied energy to be stored for potential recovery. 101 In the discharging stage, similar losses prevent complete recovery of the energy that is stored. Though decreasing the extent of salt removal and current density can reduce the magnitude of irreversible losses-allowing for a greater portion of energy to be recovered-achieving a near ideal reversible CDI process would necessitate infinitely long cycle times.…”

Dual‐Zinc Electrode Electrochemical Desalination

“…However, the capital investments, operating costs, and energy consumption are still high. Capacitive deionization (CDI) has been proposed as an energy‐saving and economic deionization approach . However, the removal capacity of a conventional CDI device remains very low owing to the limited ion electrosorption capacity of carbon electrode materials.…”

Short Review of Multichannel Membrane Capacitive Deionization: Principle, Current Status, and Future Prospect

“…Since the charge efficiency shows the degree of electric charge utilized to remove the ions, it is a major index to determine the presence of parasite reactions as well as energy consumption [40]. The energy consumption in kT is the thermodynamic energy consumption based on the specific Gibbs free energy of separation, offering the scientific evidence to compare the energy efficiency of CDI systems with that of other desalination technologies [41].…”