Water Desalination By Pseudocapacitive Deionization

Tuesday, 3 October 2017: 16:00
Chesapeake 12 (Gaylord National Resort and Convention Center)
T. Kim, C. A. Gorski, and B. E. Logan (The Pennsylvania State University)
Capacitive deionization (CDI) is an electrochemical desalination process based on electrochemical principles that involves storing ions inside pores of capacitive, carbon-based electrodes. Although there have been intensive efforts for improving CDI performance, its broader application has been limited due to the low charge storage capacities of carbon-based electrodes. However, pseudocapacitive electrode materials could provide a higher capacity for salt removal because they can undergo both faradaic ion insertion and surface capacitive reactions. For example, sodium manganese oxide can double the amount of removed ions per mass of both electrodes (mg/g) compared to activated carbon. Despite its promising performance, little work has been done mainly because most known pseudocapacitive materials undergo reactions with cations, but not anions (e.g., Cl). Therefore, precious silver metal or anion-exchange membrane-assisted carbon electrodes were necessary, which increased costs and reduced salt adsorption capacities. To overcome these limitations, we developed a system that uses two identical pseudocapacitive electrodes in two channels divided by an anion-exchange membrane. Based our success in using this system for power generation from salinity gradients, and supported by theoretical and experimental demonstrations of this concept for water desalination by others, we conducted tests to show that our system could improve desalination performance compared to previous capacitive approaches. Tests with this flow cell produced a salt adsorption capacity of the electrodes of ~40 mg/g, which is much higher than typical values reported using carbon electrodes (<20 mg/g). The cell voltage is also less than a half of typical CDI systems. Based on this high salt adsorption capacity and low applied cell voltage, this type of pseudocapacitive system could represent the next generation of low energy electrochemical process for water desalination.