Eran Avraham

Limitation of Charge Efficiency in Capacitive Deionization I. On the Behavior of Single Activated Carbon

In this paper we report on attempts to improve the efficiency of electrochemical capacitive deionization (CDI) by understanding the relevant ion adsorption processes. Specially designed three-electrode cells were elaborated to study the relationship between the charge injected and the charge efficiency of the adsorption/desorption of Na + and Cl - ions onto highly porous, high surface area carbon cloth electrodes. The counter electrodes in these cells were large reversible Ag-AgCl electrodes. Knowing the volume and concentration of the solution and the charge and mass balance of the working and counter electrodes, the degree of cation and anion adsorptions onto the working electrode could be calculated separately as a function of the applied potential. The relevance of these data to the design of a symmetric CDI cell is briefly discussed.

Limitations of Charge Efficiency in Capacitive Deionization II. On the Behavior of CDI Cells Comprising Two Activated Carbon Electrodes

The charge efficiency of electrochemical capacitive deionization (CDI) of salty-brackish water in symmetric cells comprising activated highly porous carbon electrodes was investigated as a function of the applied potential during charging (deionization) and discharging. The charge efficiency of water CDI in such cells is highly affected by the fact that the potential applied drives always simultaneously adsorption of counterions and desorption of co-ions. A previous stage of this work concentrated in the study of single activated carbon electrodes in processes. In this study, we demonstrated that it is possible to estimate the charge efficiency of symmetric CDI cells from measurements of single electrodes. Guidelines for improving the charge efficiency in water desalination by CDI processes are outlined herein. For instance, it was demonstrated based on experimental findings that it is possible to maximize the charge efficiency by applying discharge potentials (upon regeneration) higher than zero.

The Feasibility of Energy Extraction from Acidic Wastewater by Capacitive Mixing with a Molecular‐Sieving Carbon Electrode

Capacitive mixing is a newly emerging technique for the production of renewable energy from differences in salinity, usually of wastewater streams. The method is based on the controlled mixing of two streams with different salt concentrations, which are alternatingly brought into contact with precharged porous electrodes, thus taking advantage of the fact that modification of the electrical double layer of the electrodes results in changes in the solution salinity. Usually, the renewable energy resources are seawater and river water streams. Here, we demonstrated that electrical energy can be extracted by capacitive mixing of acidic wastewater and seawater. This concept is proven by the use of proton-selective carbon as the cation-capturing electrode, fabricated by carbonization of cellulose filter paper followed by mild activation in concentrated nitric acid. Considerable energy extraction was demonstrated even if the concentration of the NaCl solution was tenfold higher than that of the acidic solution.

Bromide Ions Specific Removal and Recovery by Electrochemical Desalination

Removal and recovery of bromide ions by electro-oxidation and electro-reduction are presented using hybrid physical adsorption and capacitive deionization cells, which contain activated carbon cloth electrodes. This is a proof of concept research with results, which indicate that when comparing the removal and recovery quantities of bromide and chloride ions (starting with the same initial concentration of 0.05 M for both salts), the desalination capacity of the bromide ions is larger by almost 2 orders of magnitude than that of the chloride ions; thus, we obtained specific desalination of bromide ions from a solution containing chloride ions. Removal and recovery of 3.5 mmol of bromide ions were achieved by a working electrode with 1 g of activated carbon cloth, and the calculated energy consumption for the removal and recovery of 1 g of bromide ions was about 2.24 kJ/g.