Recently, a desalination technique based on porous carbon has been reported [1], merging together desalination process with electrochemical energy storage. Thanks to this new strategy, an important step forward, respect to other water desalination technologies, has been achieved. The principle is based on the capacitive adsorption of Na⁺ and Cl^- ions in the pores of a porous activated carbon, constituting the active material of an electrochemical double layer capacitor electrode. Differently from conventional EDLC, the active material is made in the present case as slurries flowed through an electrochemical cell to achieve a continuous desalination of seat water; such system has been named Electrochemical Flow Capacitor (ELC) [2], [3].

The objective of the study is to improve the energy efficiency of the desalination process by optimizing the cell design and by selecting the proper activated carbon. To do so, we characterized a desalinization cell using different type of electrodes using the Fe^III(CN)₆^3-/Fe_II(CN)₆^4- redox couple as an electrochemical probe. Our approach allowed to define a dimensionless number θ, which is proportional to the flow rate and inversely proportional to the potential scan rate, giving a guideline to sort out different operating regimes in the flow cell. Two operating regimes have been evidenced: a permanent regime for θ > 60, allowing for higher and efficient charge adsorption, and a non-permanent domain for θ < 60.

Références :

[1] M. E. Suss, S. Porada, X.Sun, P. M. Biesheuvel, J. Yoon and V. Presser, Energy Environ Sci., 20015, 8, 2296-2319.

[2] K. B. Hatzell, E. Iwama, A. Ferris, B. Daffos, K. Urita, T. Tzedakis,F. Chauvet, P. Taberna, Y. Gogotsi, P. Simon, Electrochemistry Communications 43 (2014) 18–21.

[3] Y. Gendel, A. K. E. Rommerskirchen, O. David, M. Wessling, Electrochemistry Communications 46 (2014) 152–156.