Perspectives on the Development and Evaluation of Electrode Materials for Electrochemical Deionization Processes

Electrochemical de-ionization processes offer great promise in complementing existing water desalination technologies in purifying water over a range of salinity values. 1, 2 Theoretical evaluations have demonstrated that these methods demonstrate higher energy efficiency and lower energy requirements in de-ionizing low salinity waters. 3, 4 In practical use, the efficiency of these systems can depend on various factors such as operating conditions, salinity of waters, occurrence of parasitic reactions, to name a few. Furthermore, the utility of deionization methods depends on their relative cost at materials, energy and lifecycle levels. In this work, we first use an assessment of electrochemical deionization methods to emphasize the need for materials research to improve the viability of these processes. We then develop a framework to evaluate efficacy of electrode materials, in these systems. We discuss the advantages and disadvantages of both capacitive and faradaic electrode materials classes used in electrochemical deionization processes. We demonstrate that solution composition largely influences the performance of each of these electrode materials classes. Specifically, the ion removal capacity and charge efficiency of these electrodes is influenced by solution composition. This reduction in performance results from a combination of several factors such as slow transport in the electrode, competing parasitic reactions or formation of surface films that reduce ion diffusion rates. Despite these challenges, the ion removal capacities achieved with faradaic electrodes often exceeds those offered by capacitive or pseudocapacitive materials. Finally, we propose alternatives such as proper selection of operating conditions, electrode structure and coatings to overcome some of the above-mentioned challenges and achieve improved removal of ions from complex water streams. References M. A. Anderson, A. L. Cudero and J. Palma, Electrochim. Acta , 55 , 3845 (2010). S. Porada, R. Zhao, A. van der Wal, V. Presser and P. M. Biesheuvel, Prog. Mater. Sci. , 58 , 1388 (2013). J. Landon, X. Gao, J. K. Neathery and K. Liu, ECS Transactions , 53 , 235 (2013). Y. Oren, Desalination , 228 , 10 (2008).