The Role of Temperature on Salt Removal Using Capacitive Deionization

Abstract

Current technologies utilized for seawater desalination, reverse osmosis (RO) and Membrane distillation (MD), are energy intensive because they operated by separating the main component water (H2O) from the salt (NaCl). Capacitive deionization (CDI), an emerging separations based technology, operates by extracting the minority component (NaCl). CDI is similar to a supercapacitors[1], where ions adsorb to the high surface area activated carbon once an electric potential is applied across the electrochemical cell (ion separation process)[2-5]. However, in place of traditional non-aqueous based electrolytes is a electrolyte comprised of sea, brackish or wastewater. More recent theoretical based studies have emphasized the role heat transfer has on ion adsorption dynamics within CDI cells[6].Traditional CDI cells operate in a cyclic process where the capacitive electrodes are brought in contact with a concentrated salt solution (e.g. brackish water) and charged. Once the charged electrodes are fully saturated with salt ions, the electrodes are regenerated through discharging the electrodes in a brine solution. Analogous to a P-V diagram for traditional heat engines, the enclosed area of the charge versus voltage represents the energy consumed during this charging-discharging process. Here we explore the effect of temperature on salt removal in a CDI cycle. Experimentally, we use traditional electrochemical characterization methods, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), to evaluate the capacitance and resistance changes with temperature. Specifically the salt adsorption capacity is shown to decrease from 13.82±1.13, to 6.58±1.01 milligram NaCl/mg carbon as the cell temperature is increased from 25oC to 45oC. 1. Hatzell, K.B., M. Boota, and Y. Gogotsi. Chemical Society Reviews, 2015. 44(23): p. 8664-8687. 2. Porada, S., R. Zhao, A. Van Der Wal, V. Presser, and P. Biesheuvel.Progress in Materials Science, 2013. 3. Hatzell, K.B., M.C. Hatzell, K.M. Cook, M. Boota, G.M. Housel, A. McBride, E.C. Kumbur, and Y. Gogotsi. Environmental science & technology, 2015. 49(5): p. 3040-3047. 4. Ren, C.E., K.B. Hatzell, M. Alhabeb, Z. Ling, K.A. Mahmoud, and Y. Gogotsi. The journal of physical chemistry letters, 2015. 6(20): p. 4026-4031. 5. Hatzell, K.B., E. Iwama, A. Ferris, B. Daffos, K. Urita, T. Tzedakis, F. Chauvet, P.-L. Taberna, Y. Gogotsi, and P. Simon. Electrochemistry Communications, 2014. 43: p. 18-21. 6. Janssen, M., A. Härtel, and R. Van Roij. Physical review letters, 2014. 113(26): p. 268501.