Achieving high water recovery in a redox-flow battery with graphite felt electrodes for brine concentration

A redox-flow battery (RFB) with a four-chamber architecture was used for efficient brine concentration with high water recovery. Hereby, the graphite felt (GF) electrodes pretreated at 400 degrees C in air for 2 hours (GF400-2) were utilized to promote the redox reactions of the ferri/ferrocyanide electrolyte in the RFB system. The GF400-2 electrodes exhibited a low charge-transfer resistance of 3.53 Omega in electrochemical impedance spectroscopy analysis, and a 4.9-fold increase in peak current observed in cyclic voltammetry analysis. When treating a 4.5 g/L NaCl solution at 0.4 V, the RFB with GF400-2 demonstrated 1.7-fold higher average salt concentration rate (ASCR) than that of the RFB without GF electrodes. Moreover, increasing the water recovery from 50% to 90% had minimal effects on the energy consumption for brine concentrations in the RFB system. This feature highlights the potential application for high water recovery in concentrating the real industrial reverse osmosis rejects (ROR). As demonstrated, the RFB with GF400-2 efficiently concentrated the ROR by a factor of 6.9, achieving a high ASCR of 138.2 mu g/min/cm(2), while exhibiting a low energy consumption of 0.71 kWh/m(3). These findings offer valuable perspectives on brine management with an energy-efficient, high-water recovery RFB, establishing its significance in this domain.