Enhancing Flow Electrode Deionization Cell Performance for Water Desalination

Abstract

Flow electrode capacitive deionization (FCDI) uses electrosorption to remove ions and particles with low voltage. Its benefits include low energy use, high recovery, simplicity, and environmental friendliness. Herein, various operating conditions of carbon-based electrodes in FCDI were studied to find optimal parameters, and a new redox couple electrode was introduced for RFD. In Chapter II, five commercial carbon products were assessed for FCDI flow electrode suitability to identify the top performer. Carbon black (CB BP and CB V), carbon nanotubes (CNT), mesoporous carbon (MC), and carbon nanofibers (CNF) were compared for electrochemical and desalination performance in SCC mode. The CB BP sample showed the highest performance among all samples due to its high surface area and small particle size that allow the ions to transfer in between the particles faster without being blocked as well as its outstanding charging/discharging process. In Chapter III, different FCDI parameters, including carbon concentration, cell voltage, and flow rate of the flow electrode, were investigated to examine their influences on desalination. Long-term operation for about 83.3 minutes of the carbon-based FCDI was evaluated using the optimal results found in the conditions of 1.5 M CB BP concentration, 1.5 V cell voltage, and 20 mL min−1 flow rate of electrode and water streams. The results showed an average salt removal rate (ASRR) of 63.7 μg cm−2 min−1, energy consumption (EC) iv of 162 kJ mol−1, and charge efficiency (CE) of 89.3%. Chapter IV studies [FcN]+/2+ redox couple-based flow electrode deionization (RFD) cell for desalination application. The prepared electrode was studied and analyzed in multiple operation conditions, including, the effect of cell voltage, flow rate of the redox couple, and initial NaCl concentration in water streams. A stability test was performed to examine the redox couple's ability for long-run operation for about 5.5 hours at 1.2 V and 25 mL min−1. The average values of the results showed an ASRR of 83.1 μg cm−2 min−1, SRE of 95.4%, EC of 125.02 kJ mol−1, and CE of 92.6%. The research findings show that [FcN]+/2+ redox couple flow electrode can maintain stability for over 5.5 hours, experiencing only a 2.7% decay.