Continuous Solar Desalination of Brackish Water via a Monolithically Integrated Redox Flow Device

Abstract

Several water/salt separation processes are currently being developed to employ sunlight for sustainable water desalination. Here, we report a redox flow process for solar desalination of brackish water, which integrated a redox flow desalination (RFD) system with an aqueous dye-sensitized solar cell (DSSC). The use of an iodide/triiodide redox electrolyte mediated light-to-electricity conversion at the photoanode and salt separation across ion-exchange membranes at relatively low voltages (< 0.5 V). The solar RFD process produced freshwater ([NaCl] < 1 g L–1) continuously from a 50-mM feed solution at 10.3 LMH productivity (L-freshwater m–2-area h–1) that increased to 28.8 LMH for a 20-mM feed solution. The process current efficiency was in the range of 73 ± 7%. The nonsolar RFD mode produced freshwater at a productivity of 41.1 LMH, energy consumption of 0.42 kWh m–3, and current efficiency of about 80%. Correlations derived for predicting the extent of salt removal for the different process parameters of the solar and nonsolar RFD processes indicated that the DSSC photocurrent is a critical factor for increasing freshwater productivity in the solar RFD mode. With further improvements in water-compatible photoanodes and redox electrolytes, the solar RFD could present a viable and sustainable approach for water desalination.