Optimized desalination performance of high voltage flow-electrode capacitive deionization by adding carbon black in flow-electrode

Abstract

Flow-electrode capacitive deionization (FCDI) is a new desalination technology that delivers sustainable desalination performance. However, higher desalination rate and charge efficiency of FCDI are still desired for practical applications. In this study, voltages greater than 1.23V – the minimum voltage for water electrolysis – were applied to enhance the driving force for ion migration and adsorption in an FCDI so as to achieve higher desalination rates. When the voltage was raised from 0.6 to 4.8V, the desalination rate increased by nearly 7 times but the charge efficiency reduced from 92% to 69.5% due to the occurrence of Faradaic reactions such as water electrolysis. The other major factor that influenced the FCDI's charge efficiency was found to be concentration diffusion of ions between the FCDI's middle chamber and the two electrode chambers. To improve the charge efficiency, carbon black (CB) particles with an average diameter of 12μm were added to the activated carbon flow electrodes at a mixing ratio of 1.5wt%. With that, the FCDI's charge efficiency increased from 83.5% to 96.5% at 2.4V. Electrochemical impedance spectrometry (EIS) analysis indicates that the addition of CB particles significantly reduced the FCDI's internal resistance, thereby leading to enhanced desalination performance.