Membrane capacitive deionization (MCDI) is an emerging technology for desalinating brackish water (i.e., total dissolved contents of 5,000 ppm or less) for agriculture, industry, and producing potable water.In the water-energy nexus, it is important to develop technologies that lower the energy requirement for treating water and to minimize the amount of water used for energy production. Because MCDI enables energy recovery after saturating the porous carbon electrodes, it has been identified as an energy efficient water desalination technique – e.g., more efficient than reverse osmosis for brackish water. From the materials view of MCDI, most research has focused on improving the performance characteristics of carbon-based electrodes for MCDI devices. However, there is a lack of systematic studies relating ion-exchange membrane attributes to MCDI performance and its energy efficiency.<br/>The talk will discuss MCDI performance with three different ion-exchange membrane chemistries (crosslinked polyaliphatic hydrocarbons, poly(arylene ether) hydrocarbons, and perfluorinated polymers). Membrane properties, such as material thickness, conductivity, and selectivity, were correlated to MCDI performance attributes – which included energy expended per ion removed, salt removal rate, and coulombic efficiency. In-situ electrochemical impedance spectroscopy and electric circuit equivalent modeling identified the sources of current distribution resistances within the MCDI cell with the different membranes. The results revealed that thinner membranes with high ionic conductivity and greater water flux reduced the energy per ion removed by 30 to 40% on average. Finally, the lower resistant and high water flux membranes enabled higher current density operation for greater salt removal rates without too much detriment to energy expended per ion removed and it kept the cell voltage low enough to mitigate parasitic reactions such as carbon corrosion and water splitting (as observed by the greater coulombic efficiency values).

Low resistant and high water flux membranes improve the energy efficiency of membrane capacitive deionization

255th National Meeting (2018)

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