Improved desalination via cell voltage extension and simultaneous energy recovery of redox flow desalination using organic supporting electrolyte

Abstract

Redox flow desalination (RFD) is a promising desalination technology based on a redox flow battery system with intervening channels for water streams. However, the RFD system suffers from a low desalination capacity because its operational cell voltage is limited to approximately 1.2 V to stably operate under a narrow potential window of water. Here, we report a novel strategy for improving the desalination performance of RFD by introducing organic supporting electrolytes for redox reactions, allowing for an extension of the operational cell voltage and effective energy recovery in the RFD system. Using an organic electrolyte (100 mM TEABF4 in acetonitrile) for sustainable redox reactions (V(acac)3-/ V(acac)3 and V(acac)3/ V(acac)3+), the maximum cell voltage was increased to 3.5 V. At an operating cell voltage of 3.0 V, the system exhibited a substantially improved salt removal rate of 2670 µg/cm2/min. This is a 40-fold improvement compared with the salt removal rate (68 µg/cm2/min) in the RFD system utilizing an aqueous supporting electrolyte (100 mM Fe(CN)63-/Fe(CN)64- in 100 mM NaCl). Moreover, with the energy recovery process, the RFD system recovered 30 % of the energy used for desalination, reducing energy consumption even at a high operating cell voltage. The results suggest that the adaptation of organic electrolytes in the RFD system can be a good approach to improve desalination performance via the extension of cell voltage and energy recovery, and it can open new routes for water desalination and environmental applications.