Solar Desalination Using Dye-Sensitized Photoanode in a Redox Flow Desalination Cell

Abstract

Water desalination is a promising technological solution for assuring water security in many parts of the world. Although conventional desalination techniques, such as thermal desalination, reverse osmosis (RO), and electrodialysis (ED), are currently in use for supplying freshwater, it may not be a sustainable solution in the long term due to the heavy reliance on fossil fuels to power the process. The desalination driven by sunlight could be a potential, energy-conserving alternative to the existing techniques. Here, we demonstrated the use of redox-active photoanode to power the water desalination. We have used a dye-sensitized photoanode (of the Grätzel cell) as one of the electrodes of a water desalination cell, in which a redox couple (I−/I3 −) mediates light-to-energy conversion and sustains ion transport and ion separation in the cell. The cell consisted of electrode channels recirculating the redox couple and feed channels fed with 50 mM NaCl, which were divided by an alternative array of anion and cation exchange membranes. The short-circuit current (J sc) achieved in the integrated solar desalination cell was 2.75 mA/cm2 using a Xenon lamp (100 mW/m2), which was significantly higher than previously reported DSSC-based solar desalination (J sc = ~ 0.1 mA/cm2 [1]). This improved current density allowed for a reduction in NaCl concentration from 50 mM in the feed to 38 mM in the effluent, indicating that integrating photon-to-electron conversion and water desalination processes within a single device is a viable approach for solar-powered water desalination.[1] Chen et al., Exploration of a photo-redox desalination generator, J. Mater. Chem. A, 2019, 7, 20169