The Origins of Low Efficiency in Electrochemical De-Ionization Systems

Competing causes of efficiency loss in electrochemical and capacitive deionization systems were studied. Specifically, we explored voltage and pH related efficiency limitations of electrochemical deionization devices by comparing operational conditions in three different practical cell architectures. Static and slurry flow electrodes based on high surface area activated carbon active materials were implemented with and without ion exchange membranes. At applied biases as low as 1 V, we observe water electrolysis, pH drift, and a reduction in overall device efficiency. The impact of dissolved oxygen in the water stream was also examined and it was determined that water electrolysis products can skew common techniques for measuring conductivity and assessing desalination performance regardless of the amount of oxygen present. Additionally, the presence of ion selective membranes impacts the retention of pH-shifting species and can improve voltage stability and performance, while slurry electrodes exhibit higher ion removal efficiency than their static equivalents. (C) 2016 The Electrochemical Society. All rights reserved.